Selective area etching of III–V semiconductors using TDMAAs and TDMASb in metalorganic molecular beam epitaxy chamber

Selective area etching of SiO2-masked GaAs using trisdimethylaminoarsenic (TDMAAs) is studied. GaAs substrates are partly masked with stripe shaped SiO2 films along the [0 1 1] and [0 1̄ 1] directions. Cross-sectional scanning electron microscopy observation shows that the etched shape depends on both the direction of the mask and substrate temperature, and is almost independent of the TDMAAs flow rate. At low substrate temperatures, the (1 1 1)B surface is preferentially formed and a V-shaped groove is formed for the [0 1 1] mask direction. With increasing substrate temperature, the V-groove changes to the channel with vertical side walls due to the drastic increase of the etching rate of (1 1 1)B. For the [0 1̄ 1] mask direction, the vertical (0 1 1) plane is formed at all temperatures. It is found that etched shapes are determined by the difference of etching rates and that etching rates are influenced by the crystal structure on the surface. On the other hand, the etching rate of GaSb by TDMASb is independent of substrate surface orientation. This is because the bond strength of GaSb is weak and the etching proceeds along the direction of molecular beams. Enhanced etching rate is observed for InP by TDMAAs, which is explained by the formation of thin InAs layer on InP due to the irradiation of As released from TDMAAs.