A THERMAL-DESORPTION INVESTIGATION OF ARSINE CHEMISORPTION ON GA-RICH AND AS-RICH GAAS(100) SURFACES

We have studied the low temperature chemisorption of arsine on the Ga and As-rich surfaces of GaAs(100) using temperature programmed desorption. Arsine desorbing from the "(4 x 6)" Ga-rich surface desorbs from both molecular (T(p) almost-equal-to 165 K) and recombinative states (T(p) = 290 and 380 K) with an estimated saturation coverage of 0.09 ML, where 1 ML = 6.26 x 10(14) atoms/cm2. A very small amount of arsine is irreversibly adsorbed (approximately 0.01 ML) as evidenced by hydrogen desorption at about 520 K. This small arsine coverage suggests that most of the Ga atoms on the Ga-rich surface are not available for arsine chemisorption. On the c(2 x 8)/(2 x 4) As-rich GaAs(100) surface roughly two times more arsine desorbs compared to the Ga-rich surface and new desorption states are seen around 230 and 460 K. This increased arsine coverage suggests that most of the exposed Ga atoms on the As-rich surface are available for chemisorption. Approximately the same amount of arsine irreversibly decomposes on the c(2 x 8)/(2 x 4) As-rich surface (compared to the Ga-rich surface), but H-2 desorption occurs from a broad peak that is centered around 600 K. On the c(4 x 4) As-rich surface, arsine decomposition is not observed and only a small amount of arsine desorption is detected. This result is to be expected since there are no exposed Ga atoms on the c(4 x 4) surface.