O. G. Koshelev

Energy Levels of Structural Defects in ZnAs2

Impurity photoconductivity and temperature-dependent Hall effect measurements were used to assess the ionization energies of acceptor levels produced in undoped and Te-doped ZnAs2 single crystals by structural defects: εa(1-4) = 0.08, 0.14, 0.26, and 0.34 eV. The nature of the structural defects responsible for these acceptor levels is discussed.

Optical absorption in monoclinic zinc diphosphide

The transmittance of β-ZnP2 crystals is measured as a function of the incident light polarization, photon energy, and sample thickness over the transmission window of the crystals. The results attest to anomalous light propagation through β-ZnP2, which is attributable to refractive-index nonuniformity. The intrinsic edge in β-ZnP2 for the E ∥ c polarization is shown to be dominated by indirect and direct allowed transitions for α below and above 1 cm−1, respectively. The 300-K indirect band gap of β-ZnP2 is evaluated.

Crystal Growth and Properties of Cd1 – xZnxAs2 Solid Solutions

Cd1 – xZnxAs2 (x = 0.03, 0.05, 0.06) single crystals are grown by the Bridgman method, and their optical absorption spectra are measured. The introduction of Zn is shown to increase the band gap of CdAs2, by up to ≃14 meV at x = 0.06. The highest content of ZnAs2 incorporated into CdAs2 is 6 mol %.

Edge absorption and light propagation in single crystals of Zn1−x Cd x As2 solid solutions

The transmittance of Zn1−xCdxAs2 anisotropic single crystals in their transparency region is found to depend on the incident light polarization, photon energy, and sample thickness. This effect is shown to be associated with light scattering in Zn1−xCdxAs2, which can be understood in terms of the crystal structure of the monoclinic crystals. The fundamental absorption edge in Zn1−xCdxAs2 is dominated by an indirect forbidden transition for the E ‖ c polarization and by a direct forbidden transition for E ⊥ c.

Optical and photoelectric properties of monoclinic Zn1 − x Cd x As2 crystals

The first data are presented on the band structure of monoclinic Zn1 − xCdxAs2 crystals. The fundamental absorption edge of Zn1 − xCdxAs2 for the E ‖ c polarization is shown to be dominated by an indirect allowed transition for absorption coefficients α‖ < 6 cm−1 and by a direct allowed transition for α‖ > 6 cm−1, both transitions involving excitonic levels. The absorption edge for E ⊥ c is due to a direct forbidden transition with the participation of excitonic levels. We have determined the band gap values for these transitions in the temperature range 80–300 K, the exciton binding energy, and the ionization energies of four deep acceptor levels produced in the band gap by structural defects.

Structural defects and band-structure parameters of CdAs2, ZnAs2, Cd1 − xZnxAs2, and Zn1 − xCdxAs2 single crystals

Structurally perfect CdAs2, ZnAs2, Cd1 − xZnxAs2, and Zn1 − xCdxAs2 single crystals have been grown, and the main parameters of their band structure have been determined. We have proposed band structure models for the crystals and presented evidence in favor of the models of structural defects responsible for the donor and acceptor levels in CdAs2, ZnAs2, Cd1 − xZnxAs2, and Zn1 − xCdxAs2.

A series of free exciton lines in zinc diarsenide

A structure corresponding to the n=1, 2, and 3 free-exciton states is observed in the optical transmission spectra of zinc diarsenide at 5 K. The band gap for E⊥C at temperatures of 5–300 K and the exciton binding energy (17.5 eV) are determined.

LATTICE DEFECTS IN UNDOPED CDAS2 MONOCRYSTALS

The spectra of optical absorption and photoconductivity of perfect CdAs2 single crystals were investigated near the intrinsic edge and in the extrinsic absorption region. The existence of three donor levels created by structural defects is established. The mechanism of defect formation is suggested: the interstitial Cdi atom in different charge states created the e1 < 0.02 eV and e3 ≅ 0.42 eV levels, the Asv vacancies created the e2 ≅ 0.26 eV level.