Comparison of two-dimensional electron gas of etched and unetched InAlAs/InGaAs/InAlAs metamorphic high electron mobility transistor structures

We present the photoluminescence (PL) and Hall studies on the two-dimensional electron gas (2DEG) of etched and unetched In0.5Al0.5As/In0.5Ga0.5As metamorphic high electron mobility transistor (mHEMT) structures. The PL technique is shown to be capable of extracting the 2DEG sheet carrier concentration in a complete mHEMT structure directly without making contacts or processing, while the Hall measurement gives a substantially higher concentration due to the parallel conduction of the heavily doped cap layer. We also report a new frequency-dependent photo-Hall technique to obtain the absorption coefficient of the In0.5Ga0.5As quantum-well channel layer.