Abstract: A first sub-collector layer functions as an inflow path of a collector current that flows in a collector layer of a heterojunction bipolar transistor. A collector ballast resistor layer having a lower doping concentration than the first sub-collector layer is disposed between the collector layer and the first sub-collector layer.

Abstract: A semiconductor device includes electrodes which contain Au and which are placed above conductive layers in a region adjacent to stacked insulating films and also includes base layers which are composed of compositionally modulated layers and which are placed between the electrodes and the conductive layers. The base layers include lateral end sections composed of single layers projecting from lateral end sections of the electrodes in the direction of the interlayer interface between the insulating films; sections which are located under the electrodes and of which a major compositional component is Ti or Ti and W; and projecting sections which project from under the electrodes in the direction of the interlayer interface between the insulating films and of which compositional components are compositionally modulated to Ti and O, to Ti, O, and N, or to Ti, W, O, and N.

Abstract: Implementations described herein generally relate to methods for forming a low-k dielectric material on a semiconductor substrate. More specifically, implementations described herein relate to methods of forming a silicon oxide film at high pressure and low temperatures. In one implementation, a method of forming a silicon oxide film is provided. The method comprises loading a substrate having a silicon-containing film formed thereon into a processing region of a high-pressure vessel. The method further comprises forming a silicon oxide film on the silicon-containing film. Forming the silicon oxide film on the silicon-containing film comprises exposing the silicon-containing film to a processing gas comprising steam at a pressure greater than about 1 bar and maintaining the high-pressure vessel at a temperature between about 100 degrees Celsius and about 500 degrees Celsius.

Abstract: A method of manufacturing a semiconductor device includes providing a substrate structure including a substrate and a semiconductor column vertically protruding from the substrate, sequentially forming a first protective layer and a second protective layer on the substrate, etching a portion of the second protective layer to expose a portion of the first protective layer on the substrate and a portion of the first protective layer on an upper surface of the semiconductor column, removing the exposed portion of the first protective layer on the substrate to expose a lower portion of the semiconductor column, removing a remaining portion of the second protective layer, and forming a first contact material layer on the substrate and in contact with the lower portion of the semiconductor column. The first contact material layer in contact with the lower portion of the semiconductor column does not increase the source series resistance.

Abstract: A method of forming a semiconductor structure includes forming a semiconductor layer stack over a substrate. The stack includes a collector layer of silicon (Si) providing a collector region for one or more bipolar junction transistors (BJTs), an emitter layer of Si providing an emitter region for the BJTs, a base layer of (SiGe) with a first germanium percentage (Ge %) providing a base region for the BJTs, and at least one additional layer of SiGe with a second Ge %. The method also includes forming vertical fins in the stack, and forming a germanium oxide (GeOx) layer over the vertical fins. The method further includes performing a thermal anneal to react at least a portion of the GeOx layer with SiGe having one of the first and second Ge % to form a self-alignment layer providing self-alignment for at least one contact to the base layer.

Abstract: Use of a single alloy conductor to form simultaneous ohmic contacts (SOC) to n- and p-type 4H—SiC. The single alloy conductor also is an effective diffusion barrier against gold (AU) and oxygen (O2) at high temperatures (e.g., up to 800° C.). The innovation may also provide an effective interconnecting metallization in a multi-level metallization device scheme.

Abstract: The present disclosure relates to semiconductor structures and, more particularly, to co-integration of self-aligned and non-self aligned heterojunction bipolar transistors and methods of manufacture. The structure includes at least two heterojunction bipolar transistor (HBT) devices integrated onto a same wafer with different epitaxial base profiles. An intrinsic base epitaxy for a second device of the at least two HBT devices acts as an extrinsic base for a first device of the at least two HBT devices.

Abstract: An HBT includes a semiconductor substrate having first and second principal surfaces opposite each other; and a collector layer, a base layer, and an emitter layer stacked in this order on the first principal surface side of the semiconductor substrate. The collector layer includes a first semiconductor layer with metal particles dispersed therein, the metal particles each formed by a plurality of metal atoms bonded with each other.

Abstract: After forming an opening extending through a (100) silicon layer and a buried insulator layer and into a (111) silicon layer of a semiconductor-on-insulator (SOI) substrate, a light-emitting element is formed within the opening. A portion of the (111) silicon layer located beneath the light-emitting element is patterned to form a patterned structure for tuning light emission characteristics and enhancing efficiency of the light-emitting element. Next, at least one field effect transistor (FET) is formed on the (100) silicon layer for driving the light-emitting element.

Abstract: A method for manufacturing a bipolar transistor, including the steps of: forming a first surface-doped region of a semiconductor substrate having a semiconductor layer extending thereon with an interposed first insulating layer; forming, at the surface of the device, a stack of a silicon layer and of a second insulating layer; defining a trench crossing the stack and the semiconductor layer opposite to the first doped region, and then an opening in the exposed region of the first insulating layer; forming a single-crystal silicon region in the opening; forming a silicon-germanium region at the surface of single-crystal silicon region, in contact with the remaining regions of the semiconductor layer and of the silicon layer; and forming a second doped region at least in the remaining space of the trench.

Abstract: Embodiments of the present disclosure are directed to infrared detector devices incorporating a tunneling structure. In one embodiment, an infrared detector device includes a first contact layer, an absorber layer adjacent to the first contact layer, and a tunneling structure including a barrier layer adjacent to the absorber layer and a second contact layer adjacent to the barrier layer. The barrier layer has a tailored valence band offset such that a valence band offset of the barrier layer at the interface between the absorber layer and the barrier layer is substantially aligned with the valence band offset of the absorber layer, and the valence band offset of the barrier layer at the interface between the barrier layer and the second contact layer is above a conduction band offset of the second contact layer.

Abstract: This disclosure relates to bipolar transistors, such as heterojunction bipolar transistors, having at a doping spike in the collector. The doping spike can be disposed relatively near an interface between the collector and the base. For instance, the doping spike can be disposed within half of the thickness of the collector from the interface between the collector and the base. Such bipolar transistors can be implemented, for example, in power amplifiers.

Abstract: A sensor includes a collector, an emitter and a base-region barrier formed as an inverted bipolar junction transistor having a base substrate forming a base electrode to activate the inverted bipolar junction transistor. A level surface is formed by the collector, the emitter and the base-region barrier opposite the base substrate such that when the level surface is exposed to charge, the charge is measured during operation of the bipolar junction transistor.

Abstract: A method of forming a semiconductor structure includes forming a first seed layer, a second seed layer and an intrinsic base spaced apart from each other and with the intrinsic base located between the first seed layer and the second seed layer on an insulator layer. The method further includes forming an emitter on the first seed layer and on a first vertical surface of the intrinsic base by epitaxially growing the emitter from the first seed layer and the first vertical surface of the intrinsic base, and forming a collector on the second seed layer and on a second vertical surface of the intrinsic base by epitaxially growing the collector from the second seed layer and the second vertical surface of the intrinsic base.

Abstract: Transistors suitable for high voltage and high frequency operation. A nanowire is disposed vertically or horizontally on a substrate. A longitudinal length of the nanowire is defined into a channel region of a first semiconductor material, a source region electrically coupled with a first end of the channel region, a drain region electrically coupled with a second end of the channel region, and an extrinsic drain region disposed between the channel region and drain region. The extrinsic drain region has a wider bandgap than that of the first semiconductor. A gate stack including a gate conductor and a gate insulator coaxially wraps completely around the channel region, and drain and source contacts similarly coaxially wrap completely around the drain and source regions.

Abstract: A conventional semiconductor device used for a power supply circuit such as a DC/DC converter has problems of heat dissipation and downsizing, in particular has the problems of heat dissipation and others in the event of downsizing. A semiconductor device has a structure formed by covering a principal surface of a semiconductor chip having the principal surface and a plurality of MIS type FETs formed over the principal surface with a plurality of metal plate wires having pectinate shapes; allocating the pectinate parts alternately in a planar view over the principal surface; and further electrically coupling the plural metal plate wires to a plurality of terminals.

Abstract: A bipolar transistor includes a semiconductor structure including an emitter area, a base area and a collector area. The emitter area is electrically connected to an emitter contact of the bipolar transistor. Further, the emitter area has a first conductivity type. The base area is electrically connected to a base contact of the bipolar transistor. Further, the base area has at least mainly a second conductivity type. The collector area is electrically connected to a collector contact of the bipolar transistor and has at least mainly the first conductivity type. Further, the collector area includes a plurality of enclosed sub areas having the second conductivity type or the base area includes a plurality of enclosed sub areas having the first conductivity type.

Abstract: A heterojunction bipolar transistor includes a ballast resistor layer of which resistance increases with an increase in temperature. The ballast resistor layer includes a first ballast resistor sub-layer having a positive temperature coefficient of resistivity in a first temperature range and a second temperature range and a second ballast resistor sub-layer having a negative temperature coefficient of resistivity in the first temperature range and a positive temperature coefficient of resistivity in the second temperature range.

Abstract: This disclosure relates to bipolar transistors, such as heterojunction bipolar transistors, having at a doping spike in the collector. The doping spike can be disposed relatively near an interface between the collector and the base. For instance, the doping spike can be disposed within half of the thickness of the collector from the interface between the collector and the base. Such bipolar transistors can be implemented, for example, in power amplifiers.

Abstract: There is disclosed a method of forming layers of either GaAs or germanium materials such as SiGe. The germanium material, for example, may be epitaxially grown on a GaAs surface. Layer transfer is used to transfer the germanium material, along with some residual GaAs, to a receiver substrate. The residual GaAs may be then removed by selective etching, with the boundary between the GaAs and the germanium material providing an etch stop.

Abstract: A semiconductor device having a p base region and an n+ emitter region that come into contact with an emitter electrode and are selectively provided in a surface layer of an n? drift layer. A gate electrode is provided on a portion of the front surface of the n? drift layer which is interposed between the n+ emitter regions, with a gate insulating film interposed therebetween. In some exemplary embodiments, an n+ buffer layer and a p collector layer which have a higher impurity concentration than the n? drift layer are sequentially provided on a surface of the n? drift layer opposite to the front surface on which the n+ emitter region is provided. The impurity concentration of the n+ buffer layer is equal to or greater than 7×1016 cm?3 and equal to or less than 7×1017 cm?3. Accordingly, it is possible to obtain high field decay resistance.

Abstract: According to one exemplary embodiment, a heterojunction bipolar transistor includes a base situated on a substrate. The heterojunction bipolar transistor can be an NPN silicon-germanium heterojunction bipolar transistor, for example. The heterojunction bipolar transistor further includes a cap layer situated on the base, where the cap layer includes a barrier region. The barrier region can comprises carbon and has a thickness, where the thickness of the barrier region determines a depth of an emitter-junction of the heterojunction bipolar transistor. An increase in the thickness of the barrier region can cause a decrease in the depth of the emitter-base junction. According to this exemplary embodiment, the heterojunction bipolar transistor further includes an emitter situated over the cap layer, where the emitter comprises an emitter dopant, which can be phosphorus. A diffusion retardant in the barrier region of the cap layer impedes diffusion of the emitter dopant.

Abstract: Embodiments of the present invention provide a bipolar transistor with low resistance base contact and method of manufacturing the same. The bipolar transistor includes an emitter, a collector, and an intrinsic base between the emitter and the collector. The intrinsic base extends laterally to an extrinsic base. The extrinsic base further includes a first semiconductor material with a first bandgap and a second semiconductor material with a second bandgap that is smaller than the first bandgap.

Abstract: A heterojunction bipolar transistor (HBT) having an emitter, a base, and a collector, the base including a first semiconductor layer coupled to the collector, the first semiconductor layer having a first bandgap between a first conduction band and a first valence band and a second semiconductor layer coupled to the first semiconductor layer and having a second bandgap between a second conduction band and a second valence band, wherein the second valence band is higher than the first valence band and wherein the second semiconductor layer comprises a two dimensional hole gas and a third semiconductor layer coupled to the second semiconductor layer and having a third bandgap between a third conduction band and a third valence band, wherein the third valence band is lower than the second valence band and wherein the third semiconductor layer is coupled to the emitter.

Abstract: A method for fabricating a photovoltaic device includes forming a patterned layer on a doped emitter portion of the photovoltaic device, the patterned layer including openings that expose areas of the doped emitter portion and growing an epitaxial layer over the patterned layer such that a crystalline phase grows in contact with the doped emitter portion and a non-crystalline phase grows in contact with the patterned layer. The non-crystalline phase is removed from the patterned layer. Conductive contacts are formed on the epitaxial layer in the openings to form a contact area for the photovoltaic device.

Abstract: Heterojunction bipolar transistors are provided that include at least one contact (e.g., collector, and/or emitter, and/or base) formed by a heterojunction between a crystalline semiconductor material and a doped non-crystalline semiconductor material layer. A highly doped epitaxial semiconductor layer comprising a highly doped hydrogenated crystalline semiconductor material layer portion is present at the heterojunction between the crystalline semiconductor material and the doped non-crystalline semiconductor material layer. Minority carriers within the highly doped epitaxial semiconductor layer have a diffusion length that is larger than a thickness of the highly doped epitaxial semiconductor layer.

Abstract: A III-nitride heterojunction power semiconductor device having a barrier layer that includes a region of reduced nitrogen content.

Abstract: A III-nitride heterojunction power semiconductor device having a barrier layer that includes a region of reduced nitrogen content.

Abstract: A method of forming a template on a silicon substrate includes providing a single crystal silicon substrate. The method further includes epitaxially depositing a layer of rare earth oxide on the surface of the silicon substrate. The rare earth oxide being substantially crystal lattice matched to the surface of the silicon substrate. The method further includes forming an aluminum oxide layer on the rare earth oxide, the aluminum oxide being substantially crystal lattice matched to the surface of the rare earth oxide and epitaxially depositing a layer of aluminum nitride (AlN) on the aluminum oxide layer substantially crystal lattice matched to the surface of the aluminum oxide.

Abstract: Structures and methods of making a heterojunction bipolar transistor (HBT) device that include: an n-type collector region disposed within a crystalline silicon layer; a p-type intrinsic base comprising a boron-doped silicon germanium crystal that is disposed on a top surface of an underlying crystalline Si layer, which is bounded by shallow trench isolators (STIs), and that forms angled facets on interfaces of the underlying crystalline Si layer with the shallow trench isolators (STIs); a Ge-rich, crystalline silicon germanium layer that is disposed on the angled facets and not on a top surface of the p-type intrinsic base; and an n-type crystalline emitter disposed on a top surface and not on the angled lateral facets of the p-type intrinsic base.

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: 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 solid state lighting package is provided. The package comprising at least one LED element positioned on a top surface of a substrate or a submount capable of absorbing light emitted by the at least one LED element; and a reflective layer, the reflective layer covering at least a portion of the top surface of the substrate or the submount, whereby at least of portion of the light emitted by the LED element is reflected by the reflective layer. A method of manufacturing a solid state lighting package comprising the reflective layer, and a method of increasing the luminous flux thereof, is also provided.

Abstract: Disclosed herein is a power semiconductor module including: a circuit board having gate, emitter, and collector patterns formed thereon; a first semiconductor chip mounted on the circuit board, having gate and emitter terminals each formed on one surface thereof, and having a collector terminal formed on the other surface thereof; a second semiconductor chip mounted on the first semiconductor chip, having a cathode terminal formed on one surface thereof, and having an anode terminal formed on the other surface thereof; a first conductive connection member having one end disposed between the collector terminal of the first semiconductor chip and the cathode terminal of the second semiconductor chip and the other end contacting the collector pattern of the circuit board; and a second conductive connection member having one end contacting the anode terminal of the second semiconductor chip and the other end contacting the emitter pattern of the circuit board.

Abstract: A process, machine, manufacture, composition of matter, and improvement thereof, and method of making and method of using the same, as well as necessary intermediates, generally relating to the field of semiconductor devices, the structure of transistors, and the structure of compound semiconductor heterojunction bipolar transistors.

Abstract: A semiconductor light emitting device (10) comprises a semiconductor structure (12) comprising a first body (14) of a first semiconductor material (in this case Ge) comprising a first region of a first doping kind (in this case n) and a second body (18) of a second semiconductor material (in this case Si) comprising a first region of a second doping kind (in this case p). The structure comprises a junction region (15) comprising a first heterojunction (16) formed between the first body (14) and the second body (18) and a pn junction (17) formed between regions of the structure of the first and second doping kinds respectively. A biasing arrangement (20) is connected to the structure for, in use, reverse biasing the pn junction, thereby to cause emission of light.

Abstract: The product of the breakdown voltage (BVCEO) and the cutoff frequency (fT) of a SiGe heterojunction bipolar transistor (HBT) is increased beyond the Johnson limit by utilizing a doped region with a hollow core that extends down from the base to the heavily-doped buried collector region. The doped region and the buried collector region have opposite dopant types.

Abstract: According to one embodiment, a semiconductor light emitting device includes a substrate, a first electrode, a first conductivity type layer, a light emitting layer, a second conductivity type layer and a second electrode. The first conductivity type layer includes a first contact layer, a window layer having a lower impurity concentration than the first contact layer and a first cladding layer. The second conductivity type layer includes a second cladding layer, a current spreading layer and a second contact layer. The second electrode includes a narrow-line region on the second contact layer and a pad region electrically connected to the narrow-line region. Band gap energies of the first contact and window layers are larger than that of the light emitting layer. The first contact layer is provided selectively between the window layer and the first electrode and without overlapping the second contact layer as viewed from above.

Abstract: Disclosed is a transistor with a raised collector pedestal in reduced dimension for reduced base-collector junction capacitance. The raised collector pedestal is on the top surface of a substrate, extends vertically through dielectric layer(s), is un-doped or low-doped, is aligned above a sub-collector region contained within the substrate and is narrower than that sub-collector region. An intrinsic base layer is above the raised collector pedestal and the dielectric layer(s). An extrinsic base layer is above the intrinsic base layer. Thus, the space between the extrinsic base layer and the sub-collector region is increased. This increased space is filled by dielectric material and the electrical connection between the intrinsic base layer and the sub-collector region is provided by the relatively narrow, un-doped or low-doped, raised collector pedestal. Consequently, base-collector junction capacitance is reduced and, consequently, the maximum oscillation frequency is increased.

Abstract: A nitride semiconductor device in which contact resistance between an ohmic electrode and an ohmic recess portion is reduced and a method of manufacturing the nitride semiconductor device are provided. The nitride semiconductor device includes: a first nitride semiconductor layer formed on a substrate; a second nitride semiconductor layer formed on the first nitride semiconductor layer and having a bandgap wider than a bandgap of the first nitride semiconductor layer; an ohmic recess portion formed in at least the second nitride semiconductor layer; and an ohmic electrode provided in contact with the ohmic recess portion. The ohmic recess portion includes a corrugated structure in at least a part of a plane in contact with the ohmic electrode.

Abstract: A lateral heterojunction bipolar transistor is formed on a semiconductor-on-insulator substrate including a top semiconductor portion of a first semiconductor material having a first band gap and a doping of a first conductivity type. A stack of an extrinsic base and a base cap is formed such that the stack straddles over the top semiconductor portion. A dielectric spacer is formed around the stack. Ion implantation of dopants of a second conductivity type is performed to dope regions of the top semiconductor portion that are not masked by the stack and the dielectric spacer, thereby forming an emitter region and a collector region. A second semiconductor material having a second band gap greater than the first band gap and having a doping of the second conductivity type is selectively deposited on the emitter region and the collector region to form an emitter contact region and a collector contact region, respectively.

Abstract: A homojunction type high-speed photodiode has an active area of greater than at least 50 microns (?m) or preferably greater than 60 microns (?m) in diameter, which has an p-i-n junction epitaxial layer formed on a semiconductor substrate and includes a first ohmic contact layer, an absorption layer, a collector layer and a second ohmic contact layer. No more absorbance occurs in the collector layer of InGaAs, by means of completely absorbing the photon energy in advance by the absorption layer in which the absorption layer has powerful optical absorption constant. Not only can the prior art problems be solved, such as surface absorbance, but also improved electron transport can be achieved by using InGaAs as the constructing material, compared to other materials. The resistance capacitance (RC) for the entire structure can be significantly reduced, and the limitations to the bandwidth resulted from the carrier transport time can be improved.

Abstract: A highly sensitive and wide spectra-range mesa type photodetector having the impurity diffusion along the mesa-sidewall is provided. A mesa-type hetero-bipolar phototransistor or photodiode having a photo-absorption layer formed by a first semiconductor layer of a first conductivity type, an anode layer (or base layer) formed by a second semiconductor layer of a second conductivity type which has an opposite polarity with the first conductivity type, a wide band gap emitter or window layer formed by the third semiconductor layer on the anode layer, and the wide band gap buffer layer of the first conductivity type which has a relatively wide band gap semiconductor as compared with the second semiconductor layer on the substrate, which also serves as the cathode layer. And the first semiconductor layer, the second semiconductor layer and the wide band gap emitter or window layer is selectively etched to form the mesa structure.

Abstract: A pnp SiGe heterojunction bipolar transistor (HBT) reduces the rate that p-type dopant atoms in the p+ emitter of the transistor out diffuse into a lowly-doped region of the base of the transistor by epitaxially growing the emitter to include a single-crystal germanium region and an overlying single-crystal silicon region.

Abstract: The invention concerns a heterojunction bipolar transistor comprising a support, and epitaxially grown from said support, at least: one collecting, respectively emitting, layer; at least one base layer; and at least one emitting, respectively collecting, layer. The collecting, respectively emitting, layer comprises: at least one first undercoat contacted with said base layer, substantially of similar composition as said emitting, respectively collecting, layer; and at least one second undercoat on the side opposite said base layer relative to said first undercoat.

Abstract: Trench-generated device structures fabricated using a semiconductor-on-insulator (SOI) wafer, design structures embodied in a machine readable medium for designing, manufacturing, or testing an integrated circuit, as well as methods for fabricating trench-generated device structures. The device structure includes a trench extending through the semiconductor and insulator layers of the SOI wafer and into the underlying semiconductor substrate, and a first doped region in the semiconductor substrate. The doped region, which extends about the trench, has a second conductivity type opposite to the first conductivity type. The device structure further includes a first contact extending from the top surface through the semiconductor and insulator layers to a portion of the semiconductor substrate outside of the doped region, and a second contact extending from the top surface through the semiconductor and insulator layers to the doped region in the semiconductor substrate.

Abstract: A bipolar transistor includes: a substrate; a collector and a base layer with a p-conductive-type, an emitter layer with an n-conductive-type. The collector layer is formed above the substrate and includes a first nitride semiconductor. The base layer with the p-conductive-type is formed on the collector layer and includes a second nit ride semiconductor. The emitter layer with the n-conductive-type is formed on the base layer and includes a third nitride semiconductor. The collector layer, the base layer and the emitter layer are formed so that crystal growing directions with respect to a surface of the substrate are in parallel to a [0001] direction of the substrate. The first nitride semiconductor includes: InycAlxcGa1-xc-ycN (0?xc?1, 0?yc?1, 0<xc+yc?1). In the first nitride semiconductor, a length of an a-axis on a surface side is longer than a length of an a-axis on a substrate side.

Abstract: A SiGe heterojunction bipolar transistor is fabricated by etching an epitaxially-formed structure to form a mesa that has a collector region, a cap region, and a notched SiGe base region that lies in between. A protective plug is formed in the notch of the SiGe base region so that thick non-conductive regions can be formed on the sides of the collector region and the cap region. Once the non-conductive regions have been formed, the protective plug is removed. An extrinsic base is then formed to lie in the notch and touch the base region, followed by the formation of isolation regions and an emitter region.

Abstract: Embodiments of the present invention provide a bipolar transistor with low resistance base contact and method of manufacturing the same. The bipolar transistor includes an emitter, a collector, and an intrinsic base between the emitter and the collector. The intrinsic base extends laterally to an extrinsic base. The extrinsic base further includes a first semiconductor material with a first bandgap and a second semiconductor material with a second bandgap that is smaller than the first bandgap.

Abstract: A III-V compound semiconductor structure comprises epitaxial structures that include an integrated pair of different types of active devices. The semiconductor structure includes a semi-insulating substrate of a compound semiconductor III-V material and a first compound semiconductor III-V epitaxial structure disposed on the substrate. A concentration profile of dopant material in the semiconductor structure decreases substantially smoothly across an interface between the substrate and the first epitaxial structure in a direction from the first epitaxial structure toward the substrate, and continues to decrease substantially smoothly from the interface with increasing depth into the substrate despite the presence of silicon or oxygen contaminant at the interface. The interface is substantially free of a second contaminant that was present, during formation of the first epitaxial structure, in a chamber in which the first epitaxial structure was formed.