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The gate orientation dependence of InGaAs/AlGaAs high electron mobility transistors (HEMTs) formed by the wet-chemical recess etching has been evaluated. The short channel effect strongly depends on the gate orientation and is significant in the order of [011], [001] and [011] oriented devices. Such orientation dependence results from a difference of the side-etching lengths, which are 0.01 µm, 0.03 µm and 0.06 µm for the [011], [001] and [011] oriented devices, respectively. The other characteristics of HEMTs such BV gd, gm and f T also depend on the gate orientation because of a difference of the recessed shape.

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The effect of DC bias on the sputter-deposition of W and W-Al on GaAs substrates was investigated. By applying a negative bias to the substrate, the concentration of impurities in the metals and at the interface, such as oxygen, was reduced, and the characteristics of the Schottky contact were improved with respect to the barrier height, the n-value and the uniformity. These results are explained by the reverse sputtering effect for the substrate. This technique was applied to the gate formation of GaAs MESFETs, and the uniformity of the threshold voltage distribution within a 2-inch wafer was much improved.