Abstract: An apparatus and method is provided that uses a simple voltage ratio technique to supply specific voltages to a voltage variable attenuator, and the gates of a GaAs RF power amplifier in order to control the efficiency of the amplifier. The output of the power amplifier is sampled and then fed back to the variable voltage attenuator as a control signal. A ratio portion of the control signal is then used to control the gate biases of the power amplifier. When the power requirements are less than maximum, the voltage ratio will become more negative, resulting in less current. As the RF output increases, the voltage ratio will become more positive. Therefore, as the DC voltage varies, the power amplifier's output power will vary accordingly providing the desired output power with enhanced efficiency.

Abstract: III-V semiconductor devices such as, e.g., MESFET, JFET, MOSFET, and IGFET devices are provided with relatively high-ohmic gates or wide gate finger widths as is desirable for maximum utilization of a semiconductor surface. For example, aluminum gate electrodes having a cross-sectional area of 1.2 square micrometer and a length of 300 micrometers or more are used. The resulting devices have unexpectedly high power handling capability.

Abstract: GaAs FETs exhibit excellent long-term stability if they have a drain ledge, a drain contact with reduced dendrite size, and a silicon nitride passivation layer. Accelerated aging tests at device case temperatures of 250 degrees C. indicate essentially no device failures after 200 hours of observation and a median failure time of approximately 500 hours.

Abstract: Power handling capability and gain of metal-semiconductor field effect devices is adversely affected by a phenomenon variously known as gate-drain avalanche or gate breakdown which occurs at elevated gate-drain voltage. Consequently, it is desirable to design devices so as to maximize gate-drain breakdown voltage V.sub.gd consistent with maximum output power capability.According to the invention, such voltage is maximized by a gate-drain configuration which involves approximate equalization of per-unit-area mobile charge in a portion of the active layer under the gate contact and in an adjoining portion between gate and drain contacts. Equalization of charge may be achieved by appropriate doping or appropriate choice of layer thickness, either alone or in combination. In particular, if dopant concentration per unit volume is essentially equal in the two portions, approximate equalization of conducting channel thickness in the two portions is called for.

Abstract: Disclosed are unipolar semiconductor devices such as, e.g., metal-semiconductor field effect transistors. The disclosed devices comprise an n- or p-type active layer on a substrate and a drain contact on the active layer.The active layer comprises two contiguous regions, namely a first, more heavily doped region which is in contact with the drain contact and a second, less heavily doped region which in a direction perpendicular to the active layer extends through the remainder of the active layer. In the disclosed configuration the more heavily doped region extends past the edge of the drain contact towards a source of free carriers such as e.g., a source contact.Devices incorporating such configuration of regions in the active layer are more resistant to burnout and are capable of operating at higher voltage and power levels.

Abstract: ZnCl.sub.2 optical fibers are advantageously used for transmission of radiation in the infrared portion of the spectrum. Losses as low as 10.sup.-3 dB/km may be obtained when radiation of wavelength between 3.0 and 4.5 microns is transmitted in such fibers. Fabrication techniques allow for the formation of graded fibers to further improve transmission characteristics.