Study of the photoluminescence spectrum in high purity CdTe (original) (raw)

Band-edge photoluminescence in CdTe

physica status solidi (b), 2006

PACS 71.35. Cc, 78.40.Fy, 78.55.Et Near band-gap photoluminescence (PL) and absorption of bulk crystals of CdTe were measured over a wide range of temperatures (4 -500 K). It is demonstrated that the high-temperature (above 150 K) PL intensity correlates with a lower quality of the samples and quasiparticle localization induced by the crystal potential fluctuations. The influence of the high absorption coefficient at the free-exciton resonance energy on the PL spectra is analytically studied by solving the diffusion-recombination equation. We show that the reabsorption of the radiation by the free-exciton states creates two illusory PL maxima. No dead surface layer is needed to explain reabsorption effects. The room-temperature PL maximum matches neither the free-exciton resonance nor the band-gap energy. The high temperature PL is explained by the recombination of electrons and holes localized on potential fluctuations.

Excitation spectra of exciton luminescence in CdTe

physica status solidi (b), 1975

Measurements of the excitation spectra (of the photoluminescence lines below the band gap of CdTe led to the identification of emissions originating from excitons bound to neutral donors, to ionized donors, and to neutral acceptors, as well as from two-electron transitions. Oscillatory variations of the free and bound exciton emission intensity with the energy change of the exciting light above the band gap and their changes with temperature indicated details of the exciton relaxation mechanisms. Mcssungen der Anregnngsspektren der Photolumineszenz von Linien unterhalb der Bandkante von CdTe fiihren zur Tdentifizierung dieser Emissionslinien. Sie werden verursacht durch die Rekombination von Exzit.onen, die an neutrale oder ionisiarte Donatoren oder an neutrale Akzeptoren gebunden sind, sowie von Zwei-Elektronen-Uhergangen. Aus dem oszillatorischen Verhalten der Lumineszenzintensitat von freien und gebundenen Exzitonen bei deran Anregungsspektren oberhalb der Bandkante nnd deren Temperaturabhangigkeit wird auf Einzelheiten der Exzitonen-Relaxationsprozesse gesch!ossen.

Photoluminescence of deep level complexes in CdTe

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2011

An inevitable property of CdTe detector-grade material is a high resistivity at room temperature. Chlorine doping is a classical method to control compensation mechanisms for reaching the high resistivity material. An alternative process has been shown to be a suitable indium-doping. Additional post-growth annealing in Cd-and Te-vapour overpressure was used to obtain high resistivity material. Low temperature photoluminescence spectra were measured. The luminescence was excited either by a red laser or by a tunable Ti-sapphire laser. A typical photoluminescence line at 1.584 eV dominates the high energy end of the luminescence spectra for high resistivity material. Several low intensity luminescence bands due to shallow (effective mass) acceptors and a relatively intensive band with well-developed optical phonon replicas connected with A-centres (complex of Cd vacancy and donor atom) were observed with zero-phonon line at 1.450 eV. In the low energy part of the measured spectral range (o 1.3 eV), not only common weak and very broad luminescence bands without phonon replicas structure were apparent, but also an unusual band with clearly resolved phonon structure with zero-phonon line at 1.287 eV. A defect similar to the A-centre could be responsible for this structure.

Photoluminescence characterization of Cd-annealing effects on high purity CdTe single crystals

Journal of Crystal Growth, 2003

The Effects of Cd-atmosphere annealing and Cd-dip treatment on high purity CdTe single crystals have been studied thoroughly. It has been presented that the Cd-dip treatment could change the dominant (A 0 , X) peak in PL spectrum for as-grown crystal into (D 0 , X) for Cd-dipped crystal. This result shows that the conductivity of specimen has been converted from p-type into n-type. By measuring the reflective spectrum of the Cd-dipped specimen, very clear freeexciton (FE) emission peak has been detected. This observation of FE emission indicates that the CdTe single crystal is of very high purity. r

Deep center luminescence in p-type CdTe

Journal of Applied Physics, 1996

The deep-level photoluminescence ͑PL͒ emission in the 1.1 eV spectral region in p-type CdTe:Cl polycrystalline samples was studied as a function of the excitation laser power and temperature. The relatively broad 1.1 eV PL band has a nonsymmetrical shape which can be easily changed by varying the excitation laser power. Detailed analysis of the line shape shows that the 1.1 eV emission contains two distinct separate bands. These two bands have their zero-phonon peaks located at 1.08 and 1.17 eV, respectively, and they have quite different half-widths. A donoracceptor ͑DA͒ pair model with a deep donor and a deep acceptor with E D and E A both Ͼ0.5 eV is proposed to explain the observed experimental findings. In this model the 1.08 and 1.17 eV bands are formed as a DA recombination between pairs of the nearest neighbors, and between pairs of the next-nearest neighbors, respectively. It is concluded that the acceptor in these pairs must be an interstitial atom. One possible realization for this kind of a DA pair is the V Te -Te i complex, where V Te is acting as a donor and Te i as an acceptor.

Donor-acceptor pair photoluminescence spectra analysis in CdTe:Ag

Journal of Applied Physics, 2003

Photoluminescence ͑PL͒ spectra of CdTe single crystals and films, undoped and Ag-doped, were studied in the range of the photon energy (h): 1.5-1.6 eV, at 10 K. Films were doped during the growth process. Thin layers of Ag were vacuum evaporated onto the surface of undoped CdTe crystals, then were submitted to thermal annealing in a N 2 ϩ2% H 2 ambient at 400°C for 3 h. PL spectra of crystals exhibit a donor-acceptor pair ͑DAP͒ emission at hϭ1.491 eV ͑named here DAP Ag 2 ) with the highest intensity with respect to other signals. The PL of films is characterized by a peak at 1.5 eV followed by several phonon replicas. In both cases, the DAP emissions are due to the Ag-impurity presence and are accompanied by phonon replicas. Unannealed intrinsic crystals exhibit a unique broad DAP Ag 1 peak at hϭ1.501 eV, and one month aged at room temperature Ag-doped crystals only display a wide DAP Ag 2 peak at hϭ1.491 eV with 65% of its initial intensity, that reflects a reduced density of Ag diffused-doping levels. The origin of DAP lines in a PL spectra of CdTe:Ag has not been completely well defined until now, and we have introduced some explanatory conclusions about and a simple model for electronic transitions. This issue is important because Ag is an everpresent residual impurity in CdTe.

Photoluminescence Properties of Z-Bands in CdTe

physica status solidi (a), 1998

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Study of point defects in CdTe and CdTe:V by cathodoluminescence

Journal of Applied Physics, 1994

Cathodoluminescence in the scanning electron microscope has been used to investigate the relationship of point defects in CdTe and CdTe:V with luminescence bands at 1.40 and 1.13 eV. V has been found to inhibit the 1.40 eV luminescence. Annealing experiments indicate that Cd and Te vacancies are involved in the mentioned emission bands.

Photoluminescence and photoelectric properties of CdTe crystals doped with Er atoms

Journal of Luminescence, 2015

The low-temperature photoluminescence (PL) and photodiffusion spectra of CdTe crystals doped with Er atoms were measured. The most intensive and narrow line in the PL spectrum is A1X-line which is caused by the emission of an exciton bound to a neutral center associated with Na residual impurity. The presence of Na atoms in CdTe:Er crystals is supported by observation of recombination between electrons of the conduction band and acceptor levels associated with these impurity atoms. Other PL bands caused by optical transition with participation of donor-acceptor pairs (DAP) are also observed. It is shown that in this case P acceptor centers and donors caused by the presence of Al atoms situated in the Cd sites take part in the recombination process. The PL bands associated with recombination of DAP which include the complex acceptor centers do not appear in the PL spectra. Our findings indicate a high optical quality of the crystals. Thus, they provide a way to improve structural properties of CdTe crystals using the ability of rare earth (RE) elements to react with residual impurities in semiconductor materials. This is a result of the manifestation of so-called "cleaning" process of the semiconductor materials by their doping with RE elements.

Analysis of the 1.55 eV PL band of CdTe polycrystalline films

Materials Science and Engineering B, 2003

Photoluminescence (PL) spectra of CdTe at low temperatures usually show a narrow band at 1.55 eV, sometimes together with phonon replicas. It has been shown that this band is associated with a transition involving an acceptor level due to a cadmium vacancy; however, there is discrepancy about the high-energy level which causes this transition. It is assumed that this high-energy level comes from the bottom of the conduction band or arises from non-excited level due to a superficial donor. In order to clarify the origin of this level, we have carried out selective pair luminescence (SPL) studies at 10 K and also analyzed the temperature dependence of PL in CdTe polycrystalline samples. Our results allowed us to conclude that the 1.55 eV PL band arises from the overlap of two bands peaking at 1.550 and 1.556 eV, respectively. The first one is associated with a donor Á/acceptor pair transition and the second one (1.556 eV) is probably due to a transition involving excitons bound to a superficial acceptor of the type Cu ' i / Á/ / V (Cd :/