EXPERIMENTAL-STUDY OF THE HYDROGEN COMPLEXES IN INDIUM-PHOSPHIDE

The structure of the H-related complexes in p-type InP and in liquid e ncapsulated Czochralski semiinsulating InP:Fe has been studied from th e vibrational absorption of their PH stretching modes. Th;he acceptor complexes are produced by plasma hydrogenation so that PD modes have b een investigated also. The study has first been performed at 6 K on th e fundamentals and on the most intense of the first overtones. The tre nds in the frequencies and widths of the PH modes of the H-acceptor co mplexes for Be, Zn, and Cd accepters are discussed and explained quali tatively. In InP:Fe, the PH intrinsic modes are sharper than those of the acceptor complexes indicating a weaker interaction with the enviro nment. This study has been followed by the measurement of the temperat ure dependence of the frequencies and of the linewidths for increasing temperatures. The frequency shifts and the broadenings of the lines a re interpreted by the temperature-dependent random dephasing of the vi bration of the high-frequency oscillators in the excited state. The an alysis shows that the PH mode in the acceptor complexes couples to TA phonons of the InP lattice while the one in the complexes involving a vacancy couples to a two TA phonon combination. The anharmonicity of t he P-H bonds is comparable to the one in phosphine. A comparison of th e anharmonicity parameters derived from the overtone measurements with those derived from the hydrogen isotope effects gives evidence of the interaction between the H atom and the lattice. The amplitude of vibr ation of the D atom is smaller than that of the H atom and this explai ns why the interaction of the D atom with the lattice is smaller. This is the reason why the width of the PD modes is smaller than that of t he corresponding PH modes. The splitting of some of the PH lines in sa mples subjected to a uniaxial stress has been studied. The splitting o f the PH;Zn mode is in full agreement with a P-H bond along a (111) ax is. The same (111) orientation of the P-H bond is also found from the splitting of a line attributed to an In vacancy ''decorated'' by a H a tom ( V-In(PH)). The splitting of the strongest line in InP:Fe leads t o its attribution to a PH mode in a cubic center containing four H ato ms (V-In (PH)(4)). The presence of this center seems to account for mo st of the hydrogen present in InP:Fe. Upon annealing of the InP:Fe sam ples, V-In(PH)(4) is a source of atomic hydrogen that can be trapped b y other defects and it can leave partially hydrogenated In vacancies.