On the microwave activity of punchthrough injection transit-time structures

The microwave properties of punchthrough injection diodes exhibiting transit-time dependent negative resistances have been investigated experimentally in both the small- and large-signal regimes. The particular devices involved were p
⁺
-n-p
⁺
, M-n-p
⁺
, and p
⁺
-ν-n-p
⁺
silicon structures. Extensive small-signal admittance measurements indicated that the negative conductance of these devices arose predominantly from the transit-time delay of carriers with nearly saturated velocities. The observed minimum negative
Q
factors and the variation of device susceptance with frequency were not, however, consistent with the most simple transit-time analysis. The temperature dependence of device admittance was principally attributable to the influence of the corresponding variation of carrier velocity versus electric field. The injection properties of the Shottky-barrier emitter in the M-n-p
⁺
structure made this device more temperature sensitive than the companion p
⁺
-n-p
⁺
structure. A comparison of device capabilities as free-running oscillators indicated that further increases in output power may result with increased n-region impurity concentrations. A large-signal effect was identified, which enabled significant power generation at frequencies less than the minimum frequency for small-signal negative resistance. Detailed measurements of device admittance and bias rectification versus RF voltage were obtained from tuned amplifier experiments. The largest Pf
²
product was achieved from a p
⁺
-ν-n-p
⁺
structure that produced 115 mW at 6.3 GHz.