Applications of ternary III-V compounds to high-speed microwave modulation

High-speed microwave modulation is obtained by exploiting the intervalley electron transfer time in certain ternary III-V compounds. Saturation of the net carrier drift velocity due to intervalley electron transfer at threshold fields below 3 kV/cm is reported in GaA1-xPxand AlxGa1-xAs for x = 0.315 ± 0.01 and 0.38 ± 0.02, respectively. The equivalent circuit of a bulk device fabricated from such material is derived and verified through small-signal RF measurements which, in addition, directly yield the high-field differential mobility and electron diffusion coefficient of the material. Operated as a microwave switch, isolation levels in excess of 20 dB with 4-dB insertion loss are reported at X-band with GaAS1-xPxdevices. It is shown that contact resistance can present serious limitations, although refinements in contacting technology should result in improved performance, making devices useable through millimeter-wave frequencies. Switching speed, the measurement of which is limited by laboratory pulse generation and detection capabilities, is estimated to be well under 200 ps and a theoretical limit of 20 ps has been predicted. The importance of this work lies in the fact that these switching speeds can be obtained with no sacrifice of incident RF power-handling capability, since there is no minority-carrier charge storage in these majority-carrier devices. In addition, the devices are stable at their transit-time frequency due to the absence of negative differential mobility in the material.