EFFECTS OF LIGHT ON A P-CHANNEL INGAP GAAS/INGAAS DOUBLE-HETEROJUNCTION PSEUDOMORPHIC MODULATION-DOPED FIELD-EFFECT TRANSISTOR/

We report on the effects of light on a p-channel In0.49Ga0.51P/GaAs/In -0.13 Ga0.87As pseudomorphic modulation-doped field effect transistor (MODFET) with a 1 mu m gate length. The threshold voltage (V-th), Obta ined in the saturation region, shows nonlinear behavior with an increa se in the incident optical power (P-opt). We obtained threshold voltag es ranging from V-tho=1.35 V at P-opt=0 mW to V-th=1.55 V at P-opt=2.1 5 mW. The photocurrent was -0.37 mA at V-gs=0 V and V-ds=-3.5 V with i ncident optical power of 2.15 mW. The photocurrent is defined as the d ifference between the drain current with optical illumination and that without optical input. The absolute value of the photocurrent increas es nonlinearly with optical power, We observed that the saturated drai n currents had a critical point at the gate-source voltage of 1.4 V. T his property is expected to be related to nonlinearly increased channe l opening under optical illumination, particularly at high gate-source voltages. The current gain cut-off frequency and the maximum frequenc y of oscillation were also observed to be improved under optical illum ination.