NITRIDATION OF GAAS SINGLE-CRYSTAL SURFACES USING HYDRAZOIC ACID AND 308 NM PHOTON BEAMS

We have investigated the nitridation of GaAs(110) and (100) by photodi ssociation of the adsorbed hydrazoic acid, HN3, at 308 nm and surface temperature of 120 K with HREELS, XPS and TDS analyses. At low coverag es, the photodissociation of HN3(a) produced mainly NH(x)(a), whereas at high coverages, the photodissociation of multilayer HN3 yielded NH( x)(a), N2(a) and N3(a) as revealed by XPS and HREELS. The TDS of the i rradiated multilayer sample gave an early N2 peak at 150 K, in additio n to the one which tracked that of the parent HN3 above 160 K. The hig h temperature TDS contained a single AsN peak at 720 K before the deco mposition of the substrate above 800 K, which yielded AsN, GaN and fra gments of GaAs. The presence of these nitrides on the surface is consi stent with the results of HREELS and XPS measurements. For GaAs(110), the decomposition products, NH(x) species formed bonds with surface As and Ga atoms as indicated by the 90 meV peak in HREELS and by the app earance of new peaks in As2p3/2 and Ga2p3/2 XPS. Annealing of the lase r-irradiated sample at 450 K caused the partial desorption of the adso rbates and the breaking of the GaAs surface bonds as well as the NH bo nd. Meanwhile, the As2p3/2 XPS peaks at 1323.7 and 1325.1 eV shifted t o 1324.5 and 1325.9 eV, respectively. The former peak is attributable to the AsN species with the N atom back-bonded to the Ga atom, while t he latter peak could be attributed to the As atoms bonded to two NH(x) species. The results for the GaAs(100) surface were similar but the r elative concentration of As nitride was generally lower, probably beca use the top layer atoms are Ga instead of As. The He(I) UP spectrum sh owed a significant surface states reduction after a GaAs(100)c(8 x 2) surface was exposed to HN3 and 308 nm photon beams and then annealed a t T(s) > 750 K.