New Developments of Less Toxic Group-V Precursors for the Metalorganic Vapour Phase Epitaxy of III–V-Semiconductors: In -Situ-Formation of As–H Functions by Thermal β-Elimination of Specific As-Trialkyl Compounds

Abstract

Thermal decomposition studies and low pressure metalorganic vapour phase epitaxy (MOVPE) growth experiments have been performed using novel, less toxic arsinetrialkyl sources, which decompose by the β-hydride elimination process. Therefore, As–H functions are automatically formed in the hot temperature zone of the MOVPE reactor to enable high quality layer deposition. Decomposition studies have been carried out under growth conditions in the MOVPE reactor by quadrupole mass spectroscopy (QMS). The β-elimination decomposition of the novel As-sources diethyltertiarybutyl-arsine (DE t BAs) and diethylisopropyl-arsine (DE i PrAs) is proven by the detection of the cracking products diethylarsine (DEAsH) and the corresponding alkene fragments isobutene ( C4H8) and propene ( C3H6), respectively. The alkene-to-radical formation for different As- and P-precursors indicate a β-elimination efficiency of about 60% for tertiarybutyl- and 40% for isopropyl-groups, whereas for ethyl groups no significant indication of a β-elimination has been observed. GaAs bulk layers were grown by using trimethylgallium (TMGa) in combination with the β-eliminating As-trialkyl sources DE t BAs and DE i PrAs, respectively, as well as by using TEAs or DEAsH, both decomposing under ethyl-radical formation. In addition, the partially fluorinated source pentafluorethyl-diisopropyl-arsine (PFED i PrAs) has been investigated, however, only an etching of the GaAs substrate surface could be detected independently of the growth conditions. The use of β-eliminating As-trialkyl compounds leads to significantly improved layer properties as compared to TEAs-grown structures. GaAs layers, grown with DE t BAs or DE i PrAs at substrate temperatures of 600–650° C and V/III ratios between 8 and 80 exhibit p-type behaviour with net carrier concentrations of 3–5×1015 cm-3 and hole mobilities of 350–400 cm2/ V·s at 300 K and 3500–4100 cm2/ V·s at 77 K. Carbon is the dominant acceptor impurity in GaAs layers at present, as determined by PL spectroscopy. These results indicate a promising potential of the class of β-eliminating As-compounds as replacements for arsine in the MOVPE.