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SnO2/CuInSe2heterojunction has been prepared by depositing the SnO2film on the bulk p-CuInSe2crystal. Deposition of SnO2thin films has been performed by means of a plasma-assisted chemical vapor deposition technique using tetrabuthyltin (TBT) and oxygen as source precursors. The SnO2thin films prepared were polycrystalline and highly oriented to (200) when deposited at temperatures higher than 400°C, while amorphous-like films were obtained at deposition temperatures lower than 380°C. The SnO2/CuInSe2heterojunction diode with amorphous-like SnO2layers exhibited rectifying properties and photovoltaic effect (Voc=200 mV, Isc=0.6 mA/cm2).

CuInSe2thin films have been prepared by chemical spray pyrolysis (CSP). Effects of substrate temperature (Ts), pH and the ion ratio (Cu/In) in the spray solution on the film properties have been investigated, and the following results have been obtained; (i) films deposited with neutralized solution (pH=4.0) exhibited chalcopyrite structure in contrast to those deposited with unneutralized one (pH=1.9) having sphalerite structure, (ii) resistivity increased with Tsfor films deposited with the unneutralized solution, while decrease of the resistivity was observed for the neutralized case, and (iii) remarkable increase of resistivity with decreasing Cu/In has been observed. Finally, the effect of pH on the rectifying property in the CuInSe2/CdS heterojunction has been presented.

Photoreflectance (PR) and Photoluminescence (PL) measurements have been performed at 77 K on single crystals of CuAlxGa1-x(S0.5Se0.5)2penternary alloys grown by the iodine chemical vapor transport method. The energies of excitons associated with uppermost valence bands have been obtained as a function of composition, and an approximately quadratic dependence has been found. Near-band-edge PL has been observed in the crystal with x?0.77, and the PL has been discussed in terms of the free exciton.

We have investigated the local structure of CuInSe2(CIS) thin films by surface-sensitive EXAFS on the Cu K- and Se K-edges using synchrotron radiation. We estimated the Cu-Se and In-Se bond lengths as a function of In/Cu ratio. The local structure of the thin film CIS is quite similar to that of the bulk chalcopyrite over a wide range of the In/Cu ratio. It is found that with decreasing the In/Cu ratio from the stoichiometric composition, the Cu-Se and In-Se bond lengths systematically deviate from those of stoichiometric bulk CuInSe2, which is attributed to the chemical disorder of the cation site in the chalcopyrite structure.

Photoreflectance (PR) has been developed as a useful technique for the characterization of chalcopyrite heteroepitaxial layers. PR measurements at 77 K have been done on CuAlSe2layers grown on GaAs and GaP substrates by means of the low-pressure metalorganic chemical vapor deposition technique. The analysis of the PR spectra in terms of transition energy, intensity and broadening parameter has led us to the successful characterization of the crystal quality, stress and the crystallographic orientation in the CuAlSe2epitaxial layer.

CuInSe2thin films were prepared on SiO2-coated sodalime glass substrate by the selenization of precursors in vacuum chamber. The deposition of In/Cu precursors was carried out with varying substrate temperature. Cu-In (In/Cu and Cu/In) precursors with or without thin Se layer (100 Å) were also prepared by varying stacking sequence of Cu and In. The structure and the morphology of In/Cu precursors have been investigated. It was found that the adhesive property of the CuInSe2film to the substrate strongly depends on precursor preparation conditions.

CuInSe2thin films have been prepared by chemical spray pyrolysis (CSP) on glass substrate from the ethanol aqueous solution containing CuCl2, InCl3and N,N-dimethylselenourea. Properlies of the CuInSe2films (electrical, structural, optical absorption and morphological properties) have been systematically studied in terms of substrate temperature (Ts), pH and the ion ratio (Cu/In) of the spray solution. Good chalcopyrite CuInSe2films with large grains have been grown using the neutralized spray solution (pH=4) at the growth temperature of 360° C. On the other hand, low values of Ts, pH and Cu/In led to the production of sphalerite films.

Electrolyte electroreflectance (ER) measurements have been carried out at room temperature (297 K) on a series of bulk single crystals of CuInSe2prepared by the normal freezing method with various Cu/In ratios. The Cu-rich crystals exhibited sharp ER peaks and the AB-transition energy is 1.026 eV, while In-rich crystals exhibited broader ER peaks and smaller AB-transition energies (1.00-1.02 eV) than those of the Cu-rich ones. The spin-orbit splitting of the uppermost valence band is 0.236 eV. The effect of the Cu/In ratio on the ER spectra is discussed in terms of the Urbach energy determined by optical absorption measurement, and the bandgap energy of the stoichiometric CuInSe2crystal is discussed.

The metalorganic molecular beam epitaxial growth of CuInSe2layers on a GaAs(100) substrate was performed at 550°C using cyclopentadienylcoppertriethylphosphine (CpCuTEP), triethylindium and selenium as source precursors. CuInSe2layers with a flat surface were successfully grown. The epilayers were examined by X-ray diffraction, photoluminescence (PL) and photoreflectance measurements. The CuInSe2layer grown under optimum conditions exhibited an exciton emission in the PL spectrum.

Heteroepitaxial growth of CuGaS2was studied by low-pressure metalorganic chemical vapor deposition using normal-tripropylgallium as a new Ga precursor, combined with cyclopentadienylcoppertriethylphosphine and ditertiarybutylsulfide. Structural and optical properties were characterized in detail. The epilayer showed the c[001]-oriented growth on both GaAs(001) and GaP(001) substrates. The lattice parameter cof the epilayers was smaller than that of the bulk single crystal. Magnitude of the residual lattice strain for CuGaS2/GaP(001) was found to be larger than that for CuGaS2/GaAs(001), even though the lattice mismatch for the former was smaller than that for the latter. The strain is considered to be introduced during cooling after the growth. A photoluminescence peak at 2.493 eV (8 K) was assigned to a free exciton emission, because the peak energy agreed with A-exciton energy obtained from photoreflectance spectra.

We optimized the overall process of heteroepitaxial growth of wide-gap Cu-III-VI2chalcopyrite semiconductors by using the low-pressure metalorganic vapor phase epitaxy technique, and obtained very high quality epilayers of them. All end-point compounds, namely CuGaSe2, CuGaS2, CuAlSe2and CuAlS2, exhibited predominant free and bound excitonic photoluminescence (PL) peaks at low temperature. The color of the emission varied from red to ultraviolet. The room temperature (RT) PL spectra exhibited predominant near-band-edge emission except for that for CuAlSe2. A noticeable excitonic feature was found in the PL spectra for CuAlS2and CuGaS2even at RT. Time-resolved and excitation intensity-dependent PL measurements revealed the existence of free-to-bound (FB) and donor-acceptor pair recombination emission centers in some undoped and impurity-doped compounds and alloys. The ionization energy of the recombination centers increased with increasing band gap energy of the matrix, reflecting an increase in the hole effective mass. The potential of heteroepitaxial layers of chalcopyrite semiconductors as new light-emitting materials was demonstrated.

Near-infrared photoluminescence (PL) has been studied in CuGaS2, AgGaSe2and AgGaS2crystals doped with Yb. Sharp PL lines are observed in the 1.0 µm region for these crystals. These PL lines are assigned to 2F5/2? 2F7/2transition of the spin-orbit split states of the Yb3+ion in the chalcopyrite crystal lattice.

Electroreflectance measurements were performed on In1-xGaxP1-yAsyquaternary alloys grown on (100) GaAs by liquid-phase epitaxy in order to determine the precise band gap (E0) and broadening parameter (?). It was found that the band gap energies obtained by photoluminescence measurements differ slightly from the precise energy gap determined by ER measurements. The broadening parameters in the ER spectra of In1-xGaxP0.7As0.3LPE layers inside the miscibility gap of this alloy system are comparable with those of In1-xGaxP0.96As0.04LPE layers, and hence the LPE growth is less affected by the immiscibility, suggesting that the extraordinarily broadened band-edge luminescence in In1-xGaxP0.7As0.3is not due to the local distribution of the energy gap caused by the immiscibility. The effects of the immiscibility on the ER spectra are discussed in connection with the LPE growth conditions.

The growth of CuGaSe2films on a GaAs(100) substrate using cyclopentadienylcoppertriethylphosphine (CpCuTEP) as a Cu source in metalorganic molecular beam epitaxy (MOMBE) has been studied. Epitaxial CuGaSe2films have been grown at 500°C with the c-axis normal to the substrate plane. Films were characterized by scanning electron microscopy, X-ray diffraction, photoluminescence and photoreflectance techniques.

Photoreflectance (PR) spectra have been measured at room temperature for single crystals of CuAlxGa1-xSe2alloys grown by the chemical vapor transport method. Exciton transition energies related to valence-to-conduction bands at room temperature (EA, EBand ECin eV) have been determined as a function of composition as EA=2.654x+ 1.674(1-x)-0.22x(1-x), EB=2.767 x+ 1.749(1-x)-0.17x(1-x) and EC=2.923x+1.972(1-x)-0.32x(1-x). The PR results are discussed in terms of PL spectra.

The growth conditions have been studied in detail for InGaPAs LPE layers grown on (100) GaAs substrates using the two-phase melt technique. The accurate liquidus isotherms and iso-concentration curves have been obtained experimentally and are compared with the calculated ones. It has been found that the area of the successful growth of InGaPAs on GaAs shifts according to the degree of supercooling. The influences of variations of the As atomic fraction in the liquid, XAsl, on the liquidus and solidus compositions have also been investigated in detail. The diffusion coefficients of P and Ga in an In-rich melt at 800°C have been determined as 1.9×10-4and 1.8×10-4cm2/s, respectively. The influence of the degree of supercooling on crystal growth is discussed using a mass transport analysis in both liquid and solid phases, together with the equilibrium phase diagram.

In1-xGaxP0.96As0.04LPE layers were grown on (100) GaAs substrates from a two-phase solution with an excess GaP source at 785°C and 795°C. The relations between the liquid compositions of Ga and P, XGaland XPl, at 800°C, were obtained experimentally for a liquid composition of As, XAsl, of 0.76 at%. Based on these results, it was found that high-quality InGaPAs LPE-layers can be grown from an In melt with XGalbetween 1.10 at% and 1.30 at% and XPlbetween 2.85 at% and 2.90 at%. The liquid and solid compositions are discussed in connection with the calculated In-Ga-P-As phase diagram. The characteristics of the solution were examined by changing the growth time and temperature, and the crystal quality of the InGaPAs LPE layers was examined by a photoluminescence method in terms of the lattice mismatch between the InGaPAs LPE layer and the GaAs substrate