CHARACTERIZATION OF SURFACE-UNDOPED IN0.52AL0.48AS/IN0.53GA0.47AS/INP HIGH ELECTRON-MOBILITY TRANSISTORS

High-performance 0.3 jim gate length surface-undoped In0.52Al0.48As/In0.53Ga0.47As/InP high electron mobility transistors (HEMT) grown by MBE have been characterized and compared with surface-doped structure. At 18 GHz, the surface-undoped HEMT has achieved a maximum stable gain (MSG) of 19.2 dB compared to 16.0 dB for the surface-doped structure. The higher MSG value of the surface-undoped HEMT’s is obtained due to the improved gm/g0 ratio associated with the surface-induced electric field spreading effect. Comparison of identical 0.3 × 150 µm gate devices fabricated on surface-undoped and -doped structures has shown greatly improved gate leakage characteristics and much lower output conductance for the surface-undoped structure. The surface potential, modulated by different surface layer designs, affects the charge control in the conducting channel, especially the carrier injection into the buffer, resulting in excess output conductance as demonstrated in this study. Several millimeter-wave Coplanar Wave Guide (CPW) monolithic distributed amplifiers have been successfully fabricated by using the surface-undoped HEMT structure. The highest gain per stage distributed amplifier with 17 ± 1 dB small-signal gain across a frequency band of 24-40 GHz, the first W-band monolithic integrated circuit with 6.4-dB gain at 94 GHz, and the broadest bandwidth distributed amplifier with 5-dB gain across a frequency band of 5 to 100 GHz have been demonstrated by using the surface-undoped structures. © 1990 IEEE