Efficiency of arsenic and phosphorus precursors investigated by reflectance anisotropy spectroscopy

Abstract

The efficiency of several alternative group-V precursors was measured throught the As or P related structures in the reflectance anisotropy spectra from (001) surfaces of GaAs and InP. As arsenic precursors were investigated: arsine (AsH 3), tertiarybutylarsine (tBAsH 2) and triethylarsine (TEAs). The strength of the As-related feature at 2.5 eV in the reflectance anisotropy spectroscopy (RAS) spectrum of the typical metalorganic vapour phase epitaxy (MOVPE) pregrowth surface GaAs(001)-c(4 × 4) was measured as a function of precursor partial pressure and temperature. From these measurements, a relative efficiency for the arsenic supplied to the surface for the different precursors can be given. A higher efficiency of tBAsH 2 as compared to AsH 3 at 723 and 823 K, but equal efficiencies at 923 K, for both compounds are observed. For TEAs at lower temperatures (723 to 823 K), a new RAS spectrum different from the one for the c(4 × 4) is obtained. This reveals a surface different from the As double layer due to TEAs derivatives absorbed on the surface. At higher temperatures (923 K), a c(4 × 4)-like RAS spectrum is obtained indicating that at this temperature predominantly As is supplied from TEAs to the surface. Using both TEAs and AsH 3 simultaneously, the additional adsorbate structure disappears also at lower temperatures. This effect is attributed to the reaction of atomic hydrogen, derived from arsine, with the organic TEAs derivatives. The efficiencies of the alternative P precursors were evaluated through the P-related peak at 2.7 eV in the RAS spectrum of the phosphorus-rich InP(001)-(2 × 4). At a temperature of 873 K, the precursor tertiarybutylphosphine tBPH 2 revealed a much higher P efficiency than PH 3. In contrast, with tetraethyldiphosphine (TEDP) no P-rich (2 × 4)-like spectrum could be obtained but rather an In-rich (4 × 2) spectrum was indicated. This reveals a much lower P efficiency for TEDP than for two other P precursors. Accordingly, TEDP seems to be less well suited for MOVPE of P-containing compounds than tBPH 2.