High breakdown voltage InGaAs/InAlAs HFET using In0.56Ga0.5P spacer layer

A highly strained In_0.5Ga_0.5P spacer is introduced into an HFET grown by MOVPE on InP substrate for the first time. Despite the large lattice mismatch and the group V exchange at the channel-spacer interface the transport data are not affected ( mu _H, _{300 K}=11300 cm²/Vs, n_s=2*10¹² cm^-2). However the large bandgap energy of InGaP results in improved gate leakage, drain-conductance and drain breakdown. At V_DS=10 V a voltage gain of nu _u>100 is maintained. HFETs with L_g=0.7 mu m exhibit g_m=360 mS/mm, I_D, _max(V_DS=6 V)=550 mA/mm and a cutoff frequency f_max of 150 GHz. At V_DS=5.5 V an AC output power of 0.6 W/mm is achieved indicating the capability for high power HFET application on InP substrates.