Avalanche InP/InGaAs heterojunction phototransistor

We report on the characteristics of an avalanche InP/InGaAs heterojunction phototransistor. Below the turnover voltage, the gain is bias dependent and avalanching can be used to achieve significant (
\sim5\times
) improvement in the gain-bandwidth product. The noise current in this bias region has been measured and is shown to be predominantly shot noise of the photocurrent and the leakage current. Above the turnover voltage, negative resistance is observed and extremely high gains (>10
⁴
) are achieved. In this mode, the pulse response is a narrow spike (rise time ≃ 20 ns) whose width is independent of the width of the incident optical pulse.