Luminescent purity diagnostics of ZnSe crystals

Abstract

The photoluminescence (PL) spectra of undoped ZnSe crystals obtained from the extra pure raw material with the method of vapor transport with the I 2 gas as transporter (crystals A), and ZnSe crystals grown from the same raw material with the sublimation method (crystals B), are studied in the region 500 - 1000 nm at T equals 290 and 100 K in an attempt to find the correlation between the growth methods and the PL spectra. The PL was excited with pulsed N 2 (337 nm) and continuous wave He-Cd (442 nm) and Ar + (488 nm) lasers, which made it possible to realize the cases of strong surface, weak surface (band-to-band) and weak bulk (`impurity') excitation, respectively. It is found that in the PL spectra of samples A in the case of band-to-band excitation, except the `red' band at 1.96 eV, a `green' band at 2.3 eV is observed at 100 K, and in the spectra of samples B an IR-band at 1.25 eV is observed (290 K, bulk excitation) which is much more intense than the `red' one and which disappears at 100 K. It is established that the `red' bands with hv m equals 1.96 - 1.98 eV and hv m equals 1.88 eV in crystals A at 290 K, which arise in band-to-band and `impurity' excitation, respectively, have different nature. There is reason to think that the presence of the IR-band in the PL spectra of undoped ZnSe crystals at room temperature and bulk excitation and its vanishing in reducing the temperature, are the evidence for good purity of the material under study.