EFFICIENCY OF ARSENIC AND PHOSPHORUS PRECURSORS INVESTIGATED BY REFLECTANCE ANISOTROPY SPECTROSCOPY

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 GaAs and InP. As arsenic precursors were i nvestigated: arsine (AsH3), tertiarybutylarsine (tBAsH(2)) and triethy larsine (TEAs). The strength of the As-related feature at 2.5 eV in th e reflectance anisotropy spectroscopy (RAS) spectrum of the typical me talorganic vapour phase epitaxy (MOVPE) pregrowth surface GaAS(001)-c( 4 x 4) was measured as a function of precursor partial pressure and te mperature. From these measurements, a relative efficiency for the arse nic supplied to the surface for the different precursors can be given. A higher efficiency of tBAsH(2) as compared to AsH3 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 differe nt from the one for the c(4 x 4) is obtained. This reveals a surface d ifferent from the As double layer due to TEAs derivatives adsorbed on the surface. At higher temperatures (923 K), a c(4 x 4)-like RAS spect rum is obtained indicating that at this temperature predominantly As i s supplied from TEAs to the surface. Using both TEAs and AsH3 simultan eously, the additional adsorbate structure disappears also at lower te mperatures. This effect is attributed to the reaction of atomic hydrog en, derived from arsine, with the organic TEAs derivatives. The effici encies of the alternative P precursors were evaluated through the P-re lated peak at 2.7 eV in the RAS spectrum of the phosphorus-rich InP(00 1)-(2 x 4). At a temperature of 873 K, the precursor tertiary-butylpho sphine tBPH(2) revealed a much high P efficiency than PH3. In contrast , with tetraethyldiphosphine (TEDP) no P-rich (2 x 4)-like spectrum co uld be obtained but rather an In-rich (4 x 2) spectrum was indicated. This reveals a much lower P efficiency for TEDP than for two other P p recursors. Accordingly, TEDP seems to be less well suited for MOVPE of P-containing compounds than tBPH(2).