DELAY-TIME ANALYSIS OF ALGAAS INXGA1-XAS ESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-0.45) PSEUDOMORPHIC HJFETS WITH INGAAS CHANNEL GROWN UNDER SUPPRESSED IN-SURFACE SEGREGATION CONDITIONS/

This study uses delay time analysis to investigate the dependence of c urrent gain cutoff frequency (f(T)) on the In composition of an InGaAs layer grown by MBE under suppressed In surface segregation conditions for an AlGaAs/InGaAs hetero junction field effect transistor (HJFET). The experimental results show that the maximum fr is obtained at an I n composition (X-ln) of 0.30, in the range from 0.15 to 0.45. Delay ti me analysis reveals that the tendency of f(T) is determined mainly by the channel charging delay time (tau(char)) To explain the dependence of tau(char) on In composition, the novel expression for tau(char) is proposed. From this expression, it is found that the decrease in f(T) at X-ln > 0.30 is caused mainly by the increase in sheet resistance (1 /q N-s mu) of the InGaAs layer. This shows that the improved electron mobility resulting from suppression of In surface segregation is usefu l in reducing tau(char) Furthermore, use of an InGaAs layer thickness above 100 Angstrom at X(ln)greater than or equal to 0.30 can effective ly reduce tau(char). Delay time analysis also reveals that the saturat ion velocity is saturated at X-ln = 0.30 and declines at X-ln>0.35. Co nsequently optimum In composition and InGaAs thickness are proposed to be 0.30 and 110 Angstrom for an AlGaAs/InGaAs HJFET on a GaAs substra te. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.