A modified GaAs IMPATT structure for high-efficiency operation

A p⁺-n⁽⁺⁾-n-n⁺just punchthrough IMPATT structure is proposed and analyzed. This high-low junction structure differs from the Read structure in that the carrier concentration in the n-layer is high enough that the breakdown and punchthrough occur at the same time; yet it differs with the regular p⁺-n junction structure in that an additional n⁽⁺⁾-layer with prescribed carrier concentration and layer thickness is present. Tradeoffs between the efficiency and noise of this high-low junction IMPATT are presented and compared to the case of a conventional p-n junction IMPATT. It is shown that either the efficiency or noise performance can be improved, although one at the expense of the other. As an example, the maximum efficiency of a high-low junction IMPATT is improved from about 23 to 30 percent at the expense of a degradation in noise performance of 7 dB. On the other hand, the noise of an X-band diode can be improved by 6 dB with a degradation in efficiency from 23 to 12 percent. This structure should be useful for high-efficiency high-power applications where the noise specifications can be relaxed, or as local oscillators where the noise performance is important.