Gate pulse frequency-dependent kink effects in GaAs metal-semiconductor field-effect-transistors with a low-temperature-grown buffer layer

Abstract

Two kinds of kink effects (abrupt increases in pulsed drain current ID) were observed in GaAs metal–semiconductor field-effect transistors (MESFETs) with a buffer layer grown by molecular-beam epitaxy at low substrate temperature of 300 °C (LTB), when pulsed voltage trains with swinging range from threshold voltage to 0 V and 10% duty cycle were applied to gate electrode. These kink effects were not observed in dc measurement; however, they appeared with increasing frequency of those gate pulse trains. One kink effect is observed at 100 μs of the pulse width of high level Wh with the pulsed ID increase of 11% (first kink). Overshoot observed in the transient wave form suggests that this first kink effect is attributed only to capture of excess number of holes, which are generated by impact ionization along channel, into the hole trap of LTB. The lifetime of these holes is estimated to be 100 μs at least in the LTB from the discussion. The other kink effect is observed at 10 μs of Wh with the pulsed ID increase of 47% (second kink). This second kink effect is attributed to elimination of anomalous transient response of self-side-gating effect (SSGE) (side-gating effect caused by negative voltage applied to gate pad) by excess holes mentioned above. The mechanism of this transient of SSGE is discussed based on the observation of anomalous transient wave-form change with as small a time constant as 200 ns, using the model of side-gating effect proposed by Goto, Ohno, and Yano [IEEE Trans. Electron Devices ED-34, 1821 (1990)]. The lifetime of holes is estimated to be 10 μs at least in VD region smaller than the VD at which impact ionization occurs from the discussion. The observation of these kink effects gives evidence that the elimination of kink effects in dc was due to perfect recombination of free holes in all VD regions in this LTB MESFET. On the other hand, pulsed ID–VD curves were the same as ID–VD measured at 0 V of Vg in dc of the MESFETs with an i-GaAs buffer layer grown at 600 °C. Therefore, it is concluded that these frequency-dependent kink effects result only from the LTB. All kink effects are eliminated in dc measurement of this LTB MESFET. The kink effect related to SSGE, however, is observed at higher frequency in the LTB MESFET rather than in the MESFET with normal temperature grown buffer.