In0.5Ga0.5P spacer layer for high drain breakdown voltage InGaAs/InAlAs HFET on InP grown by MOVPE

InAlAs/InGaAs heterostructure field-effect transistors (HFET) lattice matched to InP-substrates are candidates for future low-noise microwave and opto-electronic integrated circuit applications. In order to combine them with metal-semiconductor-metal (MSM) detectors or laser diodes a high drain-voltage, high drain-current, low gate leakage and high voltage capability, respectively, is strongly required. Most work has been carried out on MBE grown samples with different Al- and In-content of the donor and the channel layer, respectively. Using the MOVPE technique the additional oxygen load in the InAlAs layer has to be taken into account which results in thin buffer layers. In this work we will show that highly strained In_0.5Ga_0.5P spacer layers are very attractive. Despite the large lattice mismatch and the group V exchange at the channel-spacer interface the transport data are not affected (μ_{H, 300 K}=11300 cm²/Vs, n_s =2×10¹² cm^-2). However the large band gap energy of In_0.5Ga_0.5P results in improved gate leakage, drain-conductance and drain breakdown. At V_DS=10 V a voltage gain of v_u>100 is maintained indicating the capability for high power HFET application on InP substrates