Room-temperature photoluminescence (PL) spectroscopy of II-VI semiconductor alloys has been proposed as a useful tool for determination of spatial variations in alloy concentration and impurity concentration. However, the nature of the PL recombination can affect the emission peak energy, as well as line shape. These effects in the band-edge emission of the compound II-VI semiconductor CdTe are reported here. PL measurements at 300 K were recorded from (1) highly doped n-type CdTe films grown by molecular-beam epitaxy, (2) undoped high-resistivity (p-10' -10 0cm) bulk CdTe, and (3) as-grown nominally p-type (p-10 -10' 0 cm) bulk CdTe. The dependence of PL emission intensity and line shape over a range of excitation from 0.003 -70 W/cm was studied. As the excitation power density was increased, a redshift in PL peak position was observed from all samples. PL peak position, intensity, and line-shape analysis show the highly excitonic nature of the radiative recombination in these materials, even though the free-exciton binding energy in CdTe is about 3 of kT at 300 K. In addition, the PL peak position can be more than 7 meV higher from n-type CdTe as compared to undoped CdTe.

High crystalline quality epitaxial CdTe(112)B/ZnTe films were deposited by molecular-beam epitaxy directly onto vicinal Si(112) substrates, without use of GaAs interfacial layers. The films were characterized with x-ray diffraction, optical microscopy, and wet chemical defect etching. Single crystal, twin-free CdTe(112)B films exhibit structural quality exceeding that previously reported for CdTe(112)B heteroepitaxy on GaAs/Si(112) or GaAs(112)B substrates. X-ray rocking curve full width at half-maximum of 72 arcsec for CdTe(224) reflection and near-surface etch pit densities (EPD) of 2×106 cm−2 have been observed for 8-μm-thick CdTe films. EPD depth profiles indicate that the threading dislocation density decreases with increasing II–VI epilayer thickness up to approximately 5 μm thickness and saturates at 2×106 cm−2 for thickness exceeding 5 μm. The CdTe epilayer orientation was observed to tilt 2° away from the Si(112) substrate orientation toward the [001] direction.

Articles you may be interested inEffect of donor-acceptor concentration ratios on nonradiative energy transfer in closely packed CdTe quantum dots Appl. Phys. Lett. 95, 133123 (2009); 10.1063/1.3242371Donor-acceptor pair photoluminescence spectra analysis in CdTe:Ag Selective excitation of an associate donoracceptor pair complex in iodinedoped CdTePhotoluminescence studies from 5 to 296 K have been performed on a series of iodine-doped CdTe epilayers grown by molecular beam epitaxy. The samples exhibit excess electron concentrations in the range from 8X 10"' to 3 X 1018 cme3. Bright edge emission is observed at 296 K from all samples. A deep-level band centered near 1.45 eV is observed at T< 2 10 K and increases in intensity with doping level. A correlation of growth parameters with photoluminescence data fits a model of the deep-level band being predominantly donor-acceptor pair recombination involving the shallow iodine donor (Ire) and the iodine A-center acceptor complex (VCd-I,). Zero-phonon emission related to this pair recombination occurs at 1.470 eV at 5 K. Thermal quenching of the integrated intensity of this donor-acceptor band is described by activation energies of 15 and 125 meV corresponding to thermalization of electrons from shallow I, donors to the conduction band and complete thermalization from the valence band to iodine A centers, respectively. 0 1995 American Institute of Physics.

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