Selective Lateral Etching of Al0.3Ga0.7As/GaAs Heterojunction Structure Using the Redox Solution of I₂/KI

Selective lateral etching for an Al 0.3 Ga 0.7 As/GaAs system was conducted with iodine-potassium iodide ( I 2 /KI) redox solution having high preferential etching characteristics. The selectivity of Al 0.3 Ga 0.7 As relative to GaAs varied with the molar ratio of I 2 /KI, pH, stripe direction, and stirring speed of the solution. The undercut widths of Al 0.3 Ga 0.7 As below the GaAs layer were measured by observing the etched cross-section with a scanning electron microscope. For the [100] directional stripe, the undercut width of Al 0.3 Ga 0.7 As was measured up to about 3 µ m after etching for 1 min under the etching conditions of [I 2 ]/[KI]=0.67 and pH=2.76. As a new application to the Al x Ga 1- x As/GaAs heterojunction bipolar transistor (HBT) with x ≤0.3, selective lateral etching was carried out to reduce the extrinsic base-collector capacitance of the HBT. As the result of capacitance-voltage (C-V) measurement, the base-collector capacitance of the lateral etched HBT was reduced to about 50% of that of the conventional HBT.