PROTON IMPLANTATION INTO GAAS - TRANSMISSION ELECTRON-MICROSCOPY RESULTS

Semi-insulating liquid-encapsulated Czochralski grown GaAs wafers were implanted at room temperature with protons at energies of 2, 4, and 30 keV at doses up to 1 x 10(18) cm-2. Without using further annealing treatments the samples were inspected, also using cross-sectional techniques, by transmission electron microscopy. Surface amorphization of the bombarded GaAs was found. Excess hydrogen precipitates in the form of large bubbles in the amorphous layer. Nearly spherical hydrogen bubbles were detected in the crystalline layer below the amorphous zone. At 30 keV, pressurized bubble rafts, where a certain number of bubbles are located in the plane of a microcrack, were detected. The recent observations of similar bubble rafts by Neethling and Snyman [J. Mater. Sci. 23, 2697 (1988)] and the present rafts are discussed in the light of the theoretical treatment of d'Olieslaeger et al. [Philos. Mag. B 63, 1321 (1991)]. The bubble rafts have presumably been produced by the collapse of pressurized hydrogen-filled microcracks.