Low-Level Interband Absorption in Phosphorus-Rich Gallium Arsenide-Phosphide

Abstract

The optical absorption edge of GaP is influenced in two principal ways when a few percent of the phosphorus atoms are replaced by arsenic. Besides the uniform decrease of the indirect band gap, the mixed crystal exhibits an extra absorption component. It is shown that this component is due to the no-phonon creation of free excitons and free-electron-hole pairs. Momentum is conserved through scattering at the arsenic impurities. The cross section for this process apparently decreases with increasing kinetic energy of the free excitons. In addition, the matrix element for indirect transitions assisted by the emission of LA phonons is enhanced by the decrease in the Xi e -Ti c energy separation in the mixed crystal. The replacement of phosphorus by arsenic in GaP is a relatively minor perturbation. Unlike the case of nitrogen in GaP, there is no bound state. The near-threshold absorption due to the arsenic-induced creation of free particles is only ~0.1% of that due to nitrogen substituents.

Secondary emission of excitons in CuCl polycrystals

“…The reversal of the amplitude of phonon replicas proves the growth of the excitonphonon coupling constant in CuCl polycrystals a t high temperature and high excitation, apparently due to the change of selection rules for intrinsic optical transitions nearby the defects of the structure [20]. An anomalously high intensity of the second phonon satellite of the v,-line in CuC1:S crystals, reported in [lo], is explained just in such a manner.…”

Direct Optical Observation of the SubsidiaryX1cConduction Band and Its Donor Levels in InP

“…As shown in Table I, the donorconcentration-dependent spectral shift is consistent with the Burstein shift measured in InP by Dumke, Lorenz, and Petti. 1 Thus it is clear that the initial state for the transitions we observe in the derivative spectrum is from near the Fermi level in the T lc conduction band. As expected, the structure in the derivative spectrum disappears in undoped samples.…”

“…The interband freecarrier absorption in InP has been measured by Dumke, Lorenz, and Pettit. 1 With the present measurement technique we have observed for the first time phonon structure associated with the F lc -X lc indirect transition in degenerately doped InP, as well as transitions from the r ic conduction band to donor levels associated with the subsidiary X lc conduction-band minima.…”

“…The authors are thankful to Professor D. Cribier and Professor M. Sieskind for fruitful discussions, 1 Zero-phonon and phonon-assisted optical transitions from the F ic conduction band to the subsidiary X ic conduction band and its donor levels have been observed in InP at 8°K. The X. ic -r lc interband energy is measured at 960 ±5 meV, and the binding energies of donors associated with the subsidiary X ic band are found to be 106 and 175 meV (±5 meV) for Te and Si, respectively.…”

“…1 The analytical form for the inter-conduction-band absorption becomes very involved, especially if phonon interactions and impurity scattering are accounted for. Basically, however, the strength of the free-carrier absorption process can be described as follows:…”