Abstract: A semiconductor device can include: a substrate having a first doping type; a first well region located in the substrate and having a second doping type, where the first well region is located at opposite sides of a first region of the substrate; a source region and a drain region located in the first region, where the source region has the second doping type, and the drain region has the second doping type; and a buried layer having the second doping type located in the substrate and below the first region, where the buried layer is incontact with the first well region, where the first region is surrounded by the buried layer and the first well region, and the first doping type is opposite to the second doping type.

Abstract: A Bipolar Junction Transistor with an intrinsic base, wherein the intrinsic base includes a top surface and two side walls orthogonal to the top surface, and a base contact electrically coupled to the side walls of the intrinsic base. In one embodiment an apparatus can include a plurality of Bipolar Junction Transistors, and a base contact electrically coupled to the side walls of the intrinsic bases of each BJT.

Abstract: Aspects of the invention provide a method of forming a bipolar junction transistor. The method includes: providing a semiconductor substrate including a uniform silicon nitride layer over an emitter pedestal, and a base layer below the emitter pedestal; applying a photomask at a first end and a second end of a base region; and performing a silicon nitride etch with the photomask to simultaneously form silicon nitride spacers adjacent to the emitter pedestal and exposing the base region of the bipolar junction transistor. The silicon nitride etch may be an end-pointed etch.

Abstract: A semiconductor structure for facilitating an integration of power devices on a common substrate includes a first insulating layer formed on the substrate and an active region having a first conductivity type formed on at least a portion of the first insulating layer. A first terminal is formed on an upper surface of the structure and electrically connects with at least one other region having the first conductivity type formed in the active region. A buried well having a second conductivity type is formed in the active region and is coupled with a second terminal formed on the upper surface of the structure. The buried well and the active region form a clamping diode which positions a breakdown avalanche region between the buried well and the first terminal. A breakdown voltage of at least one of the power devices is a function of characteristics of the buried well.

Abstract: Disclosed is an integrated circuit and a method of manufacturing an integrated circuit comprising a bipolar transistor, the method comprising providing a substrate comprising a pair of isolation regions separated by an active region comprising a collector; forming a base layer stack over said substrate; forming a migration layer having a first migration temperature and an etch stop layer; forming a base contact layer having a second migration temperature; etching an emitter window in the base contact layer, thereby forming cavities extending from the emitter window; and exposing the resultant structure to the first migration temperature in a hydrogen atmosphere, thereby filling the cavities with the migration layer material.

Abstract: The present invention discloses a method for manufacturing a semiconductor device comprising the steps of: forming a plurality of source and drain regions in a substrate; forming a plurality of gate spacer structures and an interlayer dielectric layer around the gate spacer structures on the substrate, wherein the gate spacer structures enclose a plurality of first gate trenches and a plurality of second gate trenches; sequentially depositing a first gate insulating layer and a second gate insulating layer, a first blocking layer and a second work function regulating layer in the first and second gate trenches; performing selective etching to remove the second work function regulating layer from the first gate trenches to expose the first blocking layer; depositing a first work function regulating layer on the first blocking layer in the first gate trenches and on the second work function regulating layer in the second gate trenches; and depositing a resistance regulating layer on the first work function regu

Abstract: Fabrication methods, device structures, and design structures for a bipolar junction transistor. An emitter is formed in a device region defined in a substrate. An intrinsic base is formed on the emitter. A collector is formed that is separated from the emitter by the intrinsic base. The collector includes a semiconductor material having an electronic bandgap greater than an electronic bandgap of a semiconductor material of the device region.

Abstract: A method for fabricating a CMOS device includes the following steps. A wafer is provided. STI is used to form at least one active area in the wafer. A silicon oxide layer is deposited onto the wafer covering the active area. A first high-k material is deposited onto the silicon oxide layer. Portions of the silicon oxide layer and the first high-k material are selectively removed, such that the silicon oxide layer and the first high-k material remain over one or more first regions of the active area and are removed from over one or more second regions of the active area. A second high-k material is deposited onto the first high-k material over the one or more first regions of the active area and onto a surface of the wafer in the one or more second regions of the active area. A CMOS device is also provided.

Abstract: A method for manufacturing a bipolar transistor includes forming a first epitaxial layer on a semiconductor substrate, forming a second epitaxial layer on the first epitaxial layer, forming an oxide layer on the second epitaxial layer, etching the oxide layer to form an opening in which the second epitaxial layer is exposed, and forming a third epitaxial layer in the opening. The first and third epitaxial layers have a first-type conductivity, and the second epitaxial layer has a second-type conductivity.

Abstract: An electronic device packaging structure is provided. The semiconductor device includes a semiconductor base, an emitter, a collector, and a gate. The emitter and the gate are disposed on a first surface of the semiconductor base. The collector is disposed on a second surface of the semiconductor base. A first passivation layer is located on the first surface of the semiconductor base surrounding the gate. A first conductive pad is disposed on the first passivation layer. A second conductive pad is disposed on the collector on the second surface. At least one conductive through via structure penetrates the first passivation layer, the first and second surfaces of the semiconductor base, and the collector to electrically connect the first and second conductive pads.

Abstract: A semiconductor device according to embodiments of the invention includes an n?-type drift region; a p-type base region formed selectively in the surface portion of the drift region; an n+-type emitter region and a p+-type body region, both formed selectively in the surface portion of base region; and an n-type shell region between the drift region and the base region, a shell region surrounding the entire region below base region. The shell region is doped more heavily than the drift region. The shell region contains an n-type impurity at an effective impurity amount of 8.0×1011 cm ?2 or smaller. A drift region exhibits a resistivity low enough to prevent the depletion layer expanding from collector region, formed on the back surface of the drift region, toward a shell region from reaching the shell region.

Abstract: A negative differential resistance (NDR) device is designed and a possible compact device implementation is presented. The NDR device includes a voltage blocker and a current blocker and exhibits high peak-to-valley current ratio (PVCR) as well as high switching speed. The corresponding process and design are completely compatible with contemporary Si CMOS technology and area efficient. A single-NDR element SRAM cell prototype with a compact size and high speed is also proposed as its application suitable for embedded memory.

Abstract: A poly-emitter type bipolar transistor includes a buried layer formed over an upper portion of a semiconductor substrate, an epitaxial layer formed on the semiconductor substrate, a collector area formed on the epitaxial layer and connected to the buried layer, a base area formed at a part of an upper portion of the epitaxial layer, and a poly-emitter area formed on a surface of the semiconductor substrate in the base area and including a polysilicon material. A BCD device includes a poly-emitter type bipolar transistor having a poly-emitter area including a polysilicon material and at least one of a CMOS and a DMOS formed on a single wafer together with the poly-emitter type bipolar transistor.

Abstract: In one embodiment, the invention is a method and apparatus for fabricating a high-performance band-edge complementary metal-oxide-semiconductor device. One embodiment of a method for fabricating a complementary metal-oxide-semiconductor device includes fabricating an n-type metal-oxide-semiconductor device using a gate first process, and fabricating a p-type metal-oxide-semiconductor device using a gate last process.

Abstract: A method for forming BiCMOS integrated circuits and structures formed according to the method. After forming doped wells and gate stacks for the CMOS devices and collector and base regions for the bipolar junction transistor, an emitter layer is formed within an emitter window. A dielectric material layer is formed over the emitter layer and remains in place during etching of the emitter layer and removal of the etch mask. The dielectric material layer further remains in place during source/drain implant doping and activation of the implanted source/drain dopants. The dielectric material layer functions as a thermal barrier, to limit out-diffusion of the emitter dopants during the activation step.

Abstract: An SOI device comprises an isolation trench defining a vertical drift zone, a buried insulating layer to which the isolation trench extends, and an electrode region for emitting charge carriers that is formed adjacent to the insulating layer and that is in contact with the drift zone. The electrode region comprises first strip-shaped portions having a first type of doping and second strip-shaped portions having a second type of doping that is inverse to the first type of doping. A first sidewall doping of the first type of doping is provided at a first sidewall of the isolation trench and a second sidewall doping of the second type of doping is provided at a second sidewall of the isolation trench. The first strip-shaped portions are in contact with the first sidewall doping and the second strip-shaped portions are in contact with the second sidewall doping.

Abstract: A plurality of bipolar transistors are formed by forming a common conduction region, a plurality of control regions extending each in an own active areas on the common conduction region, a plurality of silicide protection strips, and at least one control contact region. Silicide regions are formed on the second conduction regions and the control contact region. The second conduction regions may be formed by selectively implanting a first conductivity type dopant areas on a first side of selected silicide protection strips. The control contact region is formed by selectively implanting an opposite conductivity type dopant on a second side of the selected silicide protection strips.

Abstract: A method for forming BiCMOS integrated circuits and structures formed according to the method. After forming doped wells and gate stacks for the CMOS devices and collector and base regions for the bipolar junction transistor, an emitter layer is formed within an emitter window. A dielectric material layer is formed over the emitter layer and remains in place during etching of the emitter layer and removal of the etch mask. The dielectric material layer further remains in place during source/drain implant doping and activation of the implanted source/drain dopants. The dielectric material layer functions as a thermal barrier, to limit out-diffusion of the emitter dopants during the activation step.

Abstract: A method of fabricating a complementary metal oxide semiconductor (CMOS) structure including at least one nFET and at least one pFET located on a surface of a semiconductor substrate is provided. In accordance with the present invention, the nFET and the pFET both include at least a single gate metal and the nFET gate stack is engineered to have a gate dielectric stack having no net negative charge and the pFET gate stack is engineered to have a gate dielectric stack having no net positive charge. In particularly, the present invention provides a method of fabricating a CMOS structure in which the nFET gate stack is engineered to include a band edge workfunction and the pFET gate stack is engineered to have a ¼ gap workfunction.

Abstract: A biCMOS device including a bipolar transistor and a Polysilicon/Insulator/Polysilicon (PIP) capacitor is disclosed. A biCMOS device may have a relatively low series resistance at a bipolar transistor. A bipolar transistor may have a desirable amplification rate.

Abstract: A method comprises forming a first semiconductor device in a substrate, where the first semiconductor device comprises a gate structure, a spacer disposed on sidewalls of the gate structure, the spacer having a first thickness, and raised source and drain regions disposed on either side of the gate structure. The method further comprises forming a second semiconductor device in the substrate and electrically isolated from the first semiconductor device, where the second semiconductor device comprises a gate structure, a spacer disposed on sidewalls of the gate structure, the spacer having a second thickness less than the first thickness of the spacer of the first semiconductor device, and recessed source and drain regions disposed on either side of the gate structure.

Abstract: A method is provided for making a bipolar transistor which includes a tapered, i.e. frustum-shaped, collector pedestal having an upper substantially planar surface, a lower surface, and a slanted sidewall extending between the upper surface and the lower surface, the upper surface having substantially less area than the lower surface. The collector pedestal can be formed on a surface of a collector active region exposed within an opening extending through first and second overlying dielectric regions, where the opening defines vertically aligned edges of the first and second dielectric regions.

Abstract: A method of fabricating a transistor that includes a doped buried region within a semiconductor body. The doped buried region includes a portion having a first thickness and a second thickness, the first thickness being less than the second thickness. In one embodiment, the first thickness is about half the second thickness. The transistor also includes a collector region over the buried region, a base region within the collector region and an emitter region within the base region.

Abstract: A triple-well CMOS structure having reduced latch-up susceptibility and a method of fabricating the structure. The method includes forming a buried P-type doped layer having low resistance under the P-wells and N-wells in which CMOS transistors are formed and forming a gap in a buried N-type doped layer formed in the P-wells, the is gap aligned under a contact to the P-well. The buried P-type doped layer and gap in the buried N-type doped layer allow a low resistance hole current path around parasitic bipolar transistors of the CMOS transistors.

Abstract: An integrated circuit including a bipolar transistor with improved forward second breakdown is disclosed. In one embodiment, the bipolar transistor includes a base, a collector, a plurality of emitter sections coupled to a common emitter and a ballast emitter for each emitter section. Each ballast resistor is coupled between the common emitter and an associated emitter section. The size of each ballast resistor is selected so that the size of the ballast resistors vary across a two dimensional direction in relation to a lateral surface of the bipolar transistor.

Abstract: In an integrated circuit, a diode is interposed between the semiconductor substrate and the contact pad to an external bias voltage, and the substrate is biased at an internal voltage reference. Between each contact pad of the integrated circuit and semiconductor substrate, there is positioned a protection device against permanent overloads and a protection device against electrostatic discharges. By isolating the semiconductor substrate from the external voltages source and by placing a protection device between each contact pad and the substrate, a broad, general protection of the integrated circuit is obtained against all the destructive phenomena such as overloads, positive and negative overvoltages, polarity reversal and electrostatic discharges.

Abstract: Complementary metal-oxide-semiconductor (CMOS) integrated circuits with bipolar transistors and methods for fabrication are provided. A bipolar transistor may have a lightly-doped base region. To reduce the resistance associated with making electrical contact to the lightly-doped base region, a low-resistance current path into the base region may be provided. The low-resistance current path may be provided by a base conductor formed from heavily-doped epitaxial crystalline semiconductor. Metal-oxide-semiconductor (MOS) transistors with narrow gates may be formed on the same substrate as bipolar transistors. The MOS gates may be formed using a self-aligned process in which a patterned gate conductor layer serves as both an implantation mask and as a gate conductor. A base masking layer that is separate from the patterned gate conductor layer may be used as an implantation mask for defining the lightly-doped base region.

Abstract: A method of producing a semiconductor device includes the steps of: preparing a double SOI substrate, forming a deep trench, filling the deep trench, forming an opening, forming a cavity, depositing a polycrystalline silicon layer, and forming a bipolar transistor.

Abstract: A semiconductor device includes a bipolar transistor formed on a semiconductor substrate 1, in which a collector region 13 is formed on the semiconductor substrate 1; a first insulating layer 31 having a first opening 51 formed in a collector region 13 is formed on the surface of the semiconductor substrate 1; and a base semiconductor layer 14B is formed in contact with the collector region through the first opening 51. The base semiconductor layer 14B is formed such that the edge thereof extends onto the first insulating layer 31.

Abstract: A test structure and methods of using and making the same are provided. In one aspect, a test structure is provided that includes a first conductor that has a first end and a second conductor that has a second end positioned above the first end. A third conductor is positioned between the first end of the first conductor and the second end of the second conductor. A first electrode is coupled to the first conductor at a first distance from the third conductor and a second electrode coupled to the first conductor at a second distance from the third conductor. A third electrode is coupled to the second conductor at a third distance from the third conductor and a fourth electrode is coupled to the second conductor at a fourth distance from the third conductor. The first through fourth electrodes provide voltage sense taps and the first and second conductors provide current sense taps from which the resistance of the third conductor may be derived.

Abstract: The lateral pnp transistor encompasses a p-type semiconductor substrate, an n-type first buried region disposed on the semiconductor substrate, an n-type uniform base region disposed on the first buried region, an n-type first plug region disposed in the uniform base region, a p-type first emitter region and a first collector region disposed in and at the top surface of the uniform base region, a graded base region disposed in the uniform base region and a first base contact region disposed in the first plug region. The graded base region encloses the bottom and the side of the first main electrode region. The doping profile in the graded base region intervening between the first emitter region and the first collector region is such that the impurity concentration is gradually decreases towards the second main electrode region from the first main electrode region.

Abstract: The invention relates to a semiconductor device with a heterojunction bipolar, in particular npn, transistor with an emitter region (1), a base region (2), and a collector region (3), which are provided with respectively a first, a second, and a third connection conductor (4, 5, 6), while the bandgap of the base region (2) is lower than that of the collector region (3) or of the emitter region (1), for example owing to the use of a silicon-germanium alloy instead of pure silicon. Such a device is very fast, but its transistor shows a relatively low BVceo. In a device according to the invention, the emitter region (1) or the base region (2) comprises a sub-region (1B, 2B) with a reduced doping concentration, which sub-region (1B, 2B) is provided with a further connection conductor (4B, 5B) which forms a Schottky junction with the sub-region (1B, 2B). Such a device results in a transistor with a particularly high cut-off frequency fT but with no or hardly any reduction of the BVceo.

Abstract: A high voltage semiconductor device having a high current gain hFE is formed with a collector region (20) of a first conduction type, an emitter region (40) of the first conduction type, and a base region (30) of a second conduction type opposite to the first conduction type located between the collector region and the emitter region. The free carrier density of the base region (30) where no depletion layer is formed is smaller than the space charge density of a depletion layer formed in the base region (30).

Abstract: A strained channel MOSFET device with improved charge mobility and method for forming the same, the method including providing a first gate with a first semiconductor conductive type and second gate with a semiconductor conductive type on a substrate; forming a first strained layer with a first type of stress on said first gate; and, forming a second strained layer with a second type of stress on said second gate.

Abstract: The present invention provides a method for parallel production of an MOS transistor in an MOS area of a substrate and a bipolar transistor in a bipolar area of the substrate. The method comprises generating an MOS preparation structure in the MOS area, wherein the MOS preparation structure comprises an area provided for a channel, a gate dielectric, a gate electrode layer and a mask layer on the gate electrode layer. Further, a bipolar preparation structure is generated in the bipolar area, which comprises a conductive layer and a mask layer on the conductive layer. The mask layer is thinned in the area of the gate electrode. For determining a gate electrode and a base terminal area, common structuring of the gate electrode layer and the conductive layer is performed.

Abstract: The invention relates to a process of forming a compact bipolar junction transistor (BJT) that includes forming a self-aligned collector tap adjacent the emitter stack and an isolation structure. A base layer is formed from epitaxial silicon that is disposed in the substrate.

Abstract: A semiconductor structure comprises a buried first semiconductor layer of a first doping type, a second semiconductor layer of the first doping type on the buried semiconductor layer, which is less doped than the buried first semiconductor layer, a semiconductor area of a second doping type on the second semiconductor layer, so that a pn junction is formed between the semiconductor area and the second semiconductor layer, and a recess present below the semiconductor area in the buried first semiconductor layer, which comprises a semiconductor material of the first doping type, which can be less doped than the buried first semiconductor layer and has a larger distance to the semiconductor area of the second doping type on the second semiconductor layer, such that the breakdown voltage across the pn junction is higher than if the recess were not provided.

Abstract: A gate insulating film is formed on the principal surface of a semiconductor substrate. A silicon film is formed on the gate insulating film. Impurities are doped in the silicon film. In this case, impurities are doped into the silicon film to make a region of the silicon film in the memory cell area have a first impurity concentration and to make a region of the silicon film in the logic circuit area have a second impurity concentration lower than the first impurity concentration. The doped silicon film is patterned. In this case, the silicon film is patterned to leave word lines having the first impurity concentration and serving as gate electrodes in the memory cell area and to leave gate electrodes having the second impurity concentration in the logic circuit area.

Abstract: It is an object to suppress a change in a characteristic of a semiconductor device with a removal of a hard mask while making the most of an advantage of a gate electrode formed by using the hard mask. A gate electrode (3) is formed by etching using a hard mask as a mask and the hard mask remains on an upper surface of the gate electrode (3) at a subsequent step. In the meantime, the upper surface of the gate electrode (3) can be therefore prevented from being unnecessarily etched. The hard mask is removed after ion implantation for forming a source-drain region. Consequently, the influence of the removal of the hard mask on a characteristic of a semiconductor device can be suppressed. In that case, moreover, a surface of a side wall (4) is also etched by a thickness of (d) so that an exposure width of an upper surface of the source-drain region is increased. After the removal of the hard mask, it is easy to salicide the gate electrode (3) and to form a contact on the gate electrode (3).

Abstract: Structure and a method are provided for making a bipolar transistor, the bipolar transistor including a collector, an intrinsic base overlying the collector, an emitter overlying the intrinsic base, and an extrinsic base spaced from the emitter by a gap, the gap including at least one of an air gap and a vacuum void.

Abstract: The present invention provides a method for manufacturing a semiconductor device capable of acquiring productivity when a p-type source/drain is formed by the implantation of a BF2 and B ions. The method for manufacturing a semiconductor device includes the steps of: implanting a BF2 ion in a p-type source/drain region on a silicon substrate with an ion implantation energy of from about 10 keV to about 20 keV; implanting B ion in the p-type source/drain region with an ion implantation energy of from about 5 keV to about 10 keV; and forming a p-type source/drain by carrying out a thermal treatment.

Abstract: A method and a BICMOS structure are provided. The BiCMOS structure includes an SOI substrate having a bottom Si-containing layer, a buried insulating layer located atop the bottom Si-containing layer, a top Si-containing layer atop the buried insulating layer and a sub-collector which is located in an upper surface of the bottom Si-containing layer. The sub-collector is in contact with a bottom surface of the buried insulating layer.

Abstract: The lateral pnp transistor encompasses a p-type semiconductor substrate, an n-type first buried region disposed on the semiconductor substrate, an n-type uniform base region disposed on the first buried region, an n-type first plug region disposed in the uniform base region, a p-type first emitter region and a first collector region disposed in and at the top surface of the uniform base region, a graded base region disposed in the uniform base region and a first base contact region disposed in the first plug region. The graded base region encloses the bottom and the side of the first main electrode region. The doping profile in the graded base region intervening between the first emitter region and the first collector region is such that the impurity concentration is gradually decreases towards the second main electrode region from the first main electrode region.

Abstract: A method and structure for a bipolar transistor comprising a patterned isolation region formed below an upper surface of a semiconductor substrate and a single crystal extrinsic base formed on an upper surface of the isolation region. The single crystal extrinsic base comprises a portion of the semiconductor substrate located between the upper surface of the isolation region and the upper surface of the semiconductor substrate. The bipolar transistor further comprises a single crystal intrinsic base, wherein a portion of the single crystal extrinsic base merges with a portion of the single crystal intrinsic base. The isolation region electrically isolates the extrinsic base from a collector. The intrinsic and extrinsic bases separate the collector from an emitter. The extrinsic base comprises epitaxially-grown silicon. The isolation region comprises an insulator, which comprises oxide, and the isolation region comprises any of a shallow trench isolation region and a deep trench isolation region.

Abstract: The present invention discloses a miniaturized multi-layer coplanar wave guide low pass filter including: a substrate; a first dielectric layer formed on and enclosing said substrate; a first metallic pattern layer formed on said first dielectric layer; a second dielectric layer formed on said first metallic pattern layer; wherein several via holes being formed on said second dielectric layer; a second metallic pattern layer formed on said second dielectric layer, wherein said via holes formed on said second dielectric layer are filled up with the metal thereof; a third dielectric layer formed on said second metallic pattern layer, wherein several via holes being formed on said third dielectric layer; and a third metallic pattern layer formed on said third dielectric layer, wherein said via holes formed on said third dielectric layer are filled with the metal thereof.

Abstract: In one embodiment, a bipolar cell (31) includes a cell boundary (32) that defines a cell active area (33), a first array of bipolar transistors (41) is formed within the cell active area (33) and configured for a first function. The bipolar transistors (42) within the first array (41) are parallel to each other. The bipolar cell (31) further includes a second array of bipolar transistors (61) formed within the cell active area (33) and configured for a second function that is different than the first function. The bipolar transistors (62) within the second array (61) are parallel to each other and oriented in a different direction than the transistors (42) in the first array (41).

Abstract: A bipolar semiconductor device including a collector layer covered at a portion of an outer periphery thereof with an insulating film and having a shape extending in an upper direction and a horizontal direction, with a gap being formed between the collector layer and the insulating film, and further including a base layer and an emitter layer disposed over the collector layer, and a manufacturing method of the semiconductor device. Since the collector layer has a shape extending in a portion thereof in the upward direction and the horizontal direction, an external collector region can be deleted, and both the parasitic capacitance and the collector capacitance in the intrinsic portion attributable to the collector can be decreased and, accordingly, a bipolar transistor capable of high speed operation at a reduced consumption power can be constituted.

Abstract: A method for forming a heterojunction bipolar transistor (HBT) includes forming an etch mask atop an emitter cap layer of the HBT to expose a portion of the emitter cap layer, and selectively etching the exposed portion of the emitter cap layer to (1) form a reentry feature and (2) to expose a portion of the emitter layer. The method further includes selectively etching the exposed portion of the emitter layer to expose a portion of the base layer, and forming a metal layer over the exposed portion of the base layer and the exposed portion of the emitter cap layer.

Abstract: A method of forming a quasi-self-aligned heterojunction bipolar transistor (HBT) that exhibits high-performance is provided. The method includes the use of a patterned emitter landing pad stack which serves to improve the alignment for the emitter-opening lithography and as an etch stop layer for the emitter opening etch. The present invention also provides an HBT that includes a raised extrinsic base having monocrystalline regions located beneath the emitter landing pad stack.

Abstract: A method for forming a heterojunction bipolar transistor (HBT) includes forming an etch mask atop an emitter cap layer of the HBT to expose a portion of the emitter cap layer, and selectively etching the exposed portion of the emitter cap layer to (1) form a reentry feature and (2) to expose a portion of the emitter layer. The method further includes selectively etching the exposed portion of the emitter layer to expose a portion of the base layer, and forming a metal layer over the exposed portion of the base layer and the exposed portion of the emitter cap layer.