CuInSe2 Single Crystals Research Articles

Optical properties and grain boundary effects in CuInSe2

The optical properties of CuInSe2 thin films and single crystals are reported. The wavelength dependence of the refractive index and extinction coefficient is measured using multiple angle-of-incidence ellipsometry. Absorption coefficients as high as 6×105/cm are reported—the highest for any semiconductor. CuInSe2 is confirmed to have a room temperature, direct-bandgap transition near 0.96 eV for the single crystals, and 1.02 for the thin films. The difference is proposed to be due to nonuniformity in composition of the polycrystalline material. Additional absorption in the low absorption-coefficient regime is likely due to transitions associated with phonon absorptions for the single crystals. The effects of heat treatments in Ar, N, and O are shown to improve the optical properties of the thin films due to improvement in film compositional uniformity. Heating in high vacuum causes Se desorption near the film surface, causing a related degradation in the absorption characteristics.

Electrical properties of CuInSe2 single crystals grown by the vertical bridgman technique

Electrical properties of CuInSe2 single crystals grown by the vertical bridgman technique

EPR characterisation of p-type CuInSe2single crystals

The EPR characterisation of p-type CuInSe2 single crystals shows them to be predominantly contaminated by Fe; the Fe defect is present as a cation-substituted Fe3+ ion. The spin Hamiltonian parameters of this defect were determined at T=4.2K to be mod g/sub /// mod =2.040, mod D mod =0.3044 cm-1 and mod a+2/3F mod =0.0172 cm-1.

Preparation and Photovoltaic Properties of CdIn2S4/CuInSe2 Heterojunctions

N-CdIn2S4/p-CuInSe2 heterojunctions have been prepared by depositing CdIn2S4 films on p-type CuInSe2 single crystals. The current-voltage characteristics suggest that the tunnel-recombination process predominates in the mechanisms of passage of forward current through the heterojunctions. The capacitance-voltage characteristics of the diodes were those of an abrupt junction. An energy-band diagram for the heterojunctions is proposed. The photovoltaic properties obtained are an open-circuit voltage of 0.43 V, short-circuit current of 8.7 mA/cm2, fill factor of 0.46 and conversion efficiency of 2%. The photospectral response of the diodes, measured for light incident through the CdIn2S4 window, is fairly flat between 500 and 1200 nm. The quantum efficiency at 633 nm is 0.18.

Electrical Properties of p- and n-Type CuInSe2 Single Crystals

The electrical resistivity and Hall effect of p- and n-type CuInSe2 single crystals are measured in the temperature range from 80 K to 500 K. p- and n-type samples are prepared by doping with excess Se and excess In, respectively. The acceptor levels at 0.020 eV and 0.028 eV above the valence band and the donor levels at 0.012 eV and 0.18 eV below the conduction band are identified. The mobility data are analysed assuming scattering by acoustic, polar optical, and nonpolar optical phonons and by ionized impurities. For some of the n-type samples, the measurements are extended to liquid helium temperature and the result is analysed by the existing theories of impurity band conduction.

Photoelectromagnetic effect in CuInSe2

The photoelectromagnetic effect is studied in single crystals of CuInSe2. A region of light excitation is found in which the dependence of iPEM on light intensity is linear. From the experimental data, a lifetime of the minority carriers τn=0.6×10−9 sec and a surface recombination velocity s=3×105 cm/sec are determined.

Homojunction fabrication in CuInSe2 by copper diffusion

Rectifying p−n junctions have been fabricated in single crystals of CuInSe2 by diffusion of copper at relatively low temperatures. Some evidence of device instability at room temperature has been obtained.

Electrical properties and luminescence of CuInSe2

We have studied the electrical properties and luminescence spectra of melt-grown CuInSe2 single crystals and the doping of the crystals with intrinsic defects and extrinsic impurities. The preparation and the properties of p-n junctions are also discussed. We find that the low temperature photoluminescence spectra of crystals as-grown or annealed between 400 and 700 C are characteristic of the conductivity type. At 77 K, p-type crystals emit in a band peaked at 1.00 eV (type A spectrum) whereas the emission of n-type crystals peaks at 0.93 eV (type B spectrum). Type A and type B spectra can be interchanged by alternate anneals in minimum or maximum Se pressure. Type B emission dominates the electroluminescence spectrum of p-n junctions. These features are explained by the appearing and disappearing of a donor level as a consequence of annealing in vacuum or in Se atmosphere. We find that Zn and Cd act as donors. Crystals doped with these impurities have electron concentrations above 1018 cm−3. Zn-dopped samples exhibit a very broad recombination band below the bandgap in photoluminescence both at 77 and 300 K.