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We investigated the photogenerated carrier leakage from a Ga0.65In0.35N0.005As0.995/GaAs single quantum well (SQW) by piezoelectric photothermal (PPT) spectroscopy. The PPT measurement can detect the heat generated by a nonradiative recombination of photogenerated carriers. Hence, we could clarify the carrier confinement and leakage processes in the quantum well structure by comparing with the results of the PPT and surface photovoltage (SPV) measurements; the SPV measurement can detect a photoinduced change in the surface potential due to both the drift and accumulation of photogenerated carriers. The results showed that the carrier leakage from the SQW plays an important role in the carrier recombination mechanism, despite the high carrier confinement efficiency of SQW compound structures, which are used in laser diodes.

Structural, electrical and optical properties of Sb-doped CuInS 2 thin films grown by single source thermal evaporation method were studied. The films were annealed from 100 to 500 °C in air after the evaporation. The X-ray diffraction spectra indicated that polycrystalline CuInS 2 films were successfully obtained by annealing above 200 °C. This temperature was lower than that of non-doped CuInS 2 films. Furthermore, We found that the Sb-doped CuInS 2 thin films became close to stoichiometry in comparison with non-doped CuInS 2 thin films. The Sb-doped samples annealed above 200 °C has bandgap energy of 1.43–1.50 eV.

CuIn X Ga 1-X Se 2 (CIGS) alloys which can be used in photovoltaic applications have been prepared by a normal freezing (NF) method. The crystal structure, composition and conductivity types in the obtained CIGS crystals have been examined by X-ray diffraction (XRD), electron probe microanalysis (EPMA) and thermoprobe analysis, respectively. All samples are of the chalcopyrite structures, nearly stoichiometric and p-type. The grown CuInSe 2 (CIS) sample is of high quality since the free-exciton emission line is clearly observed in photoluminescence (PL). The CIGS samples turn out to have many acceptor-type defects because the free-to-acceptor emission bands show considerable intensities in the PL spectra.

CuInSe2 (CIS) films with Cu/In ratios of γ=0.82–1.79 have been grown on a GaAs (001) substrate by molecular beam epitaxy. Piezoelectric photoacoustic (PPA) measurements were carried out from liquid helium to room temperature to investigate nonradiative carrier recombination processes in comparison with photoluminescence (PL) measurements which directly detected radiative carrier recombination processes. Three PPA signal peaks which corresponded to band gap energies of the CIS (AB and C bands) and the GaAs substrate, were clearly obtained between liquid helium and room temperatures. A free-exciton emission line was observed up to 200 K in the PL spectra. Two additional peaks on intrinsic defects which are Cu vacancy (VCu) and interstitial In (Ini) were observed in the In-rich CIS samples. The PPA measurements were useful in investigating the defect levels and the band gap energy in the CIS/GaAs thin films.

Li-doped Zincselenide (ZnSe) single crystals with various Li concentrations were grown by the sublimation method. Three types of donor–acceptor pair (DAP) bands with their phonon replica are observed in their photoluminescence (PL) spectra at 4.2 K. As the Li concentrations increase, the DAP bands seems to shift to the lower energy side. From the excitation intensity and the temperature dependence of PL spectra, three kinds of constituent donors with the activation energies of 17, 28 and 50 meV are detected. It will be proposed that the origins of donors are Li i (Li interstitials), Cl Se (substitutional Cl in Se sites) and complex donors, respectively. These donors become dominant, in turn, to form DA pair recombination as the Li concentrations increase.

Piezoelectric photoacoustic (PA) measurements on liquid‐encapsulated‐Czochralski‐grown n‐GaAs were carried out at room temperature. A continuous broad band below 1.35 eV and a peak at 1.383 eV were observed in the PA amplitude spectra. By comparing with the optical‐absorption spectra, it is concluded that the broad band is due to the electron transition involving the EL2 deep‐lying defect levels. For the observed peak at 1.383 eV, the origin is considered to be dislocation related. The possibility that this peak is an apparent one expected from the proposed models for the PA signal generation is denied.

A CuInSe2 (CIS) film with Cu/In ratio of γ = 1.79 has been grown on (001) oriented GaAs substrate by molecular beam epitaxy (MBE) at substrate temperature of Ts = 450 °C, Piezoelectric photoacoustic (PPA) spectra were measured at liquid nitrogen and room temperatures. Two signals due to the non-radiative carrier recombination that correspond to bandgap energies of CIS and GaAs substrate were obtained. After illuminating with secondary light (λ = 1100 nm), two additional PPA peaks were observed for the CIS film at liquid nitrogen temperature. These signals are due to intrinsic defects in the Cu-rich CIS film.

The exciton binding energies (E xb) of a dilute nitride Ga1-y In y N0.012As0.988 layer (y = 0.0 to 4.5%) with the thickness of 100 nm were determined by both piezoelectric photothermal (PPT) and photoreflectance (PR) spectroscopies. Curve-fitting analyses were carried out using a three-dimensional direct allowed-transition model with the Voigt function as a convolution integral for PPT and with Aspnes' formula for PR. The observed estimation error for PR was about two times larger than that of PPT. Therefore, we conclude that PPT is a novel methodology for determining E xb when it is small and two expected critical energies exist in the narrow energy region.

Photoacoustic (PA) measurements of p- and n-type Si single crystals are carried out at liquid helium temperature (4.2 K). Two small peaks around 1.2 eV are observed in both samples. The energy of the higher-energy peak at 1.21 eV agrees with the thresholds of free exciton absorption with the emission of TO momentum-conserving phonons. The lower-energy peak shifts to the higher energy side with the decrease of the excitation light intensity. The possibility of the formation of an electron-hole drop for the lower energy peak will be discussed to explain the experimental results.

Photoacoustic (PA) measurements of p-Si single crystals annealed at 450°C were carried out at room temperature near an optical absorption edge. The height of the pronounced peak at 1.07 eV, which appears only in the p-type samples, becomes smaller and disappear with an increase in the annealing time. Since annealing facilitates the thermal donor formation, the decrease in the peak height is explained by the compensation mechanism of the boron acceptors. The reappearance of the 1.07 eV peak with further annealing at 800°C for 30 minutes, where thermal donors are swept away, firmly supports our explanation.

Room-temperature photoacoustic (PA) spectra of p-type silicon single crystals were measured by using a piezoelectric transducer as a detector. Two peaks at 1.08 and 1.20 eV were observed. Since the peak at 1.08 eV appears only in boron-doped p-type samples, we consider this peak to be due to the boron impurity level. The 1.20 eV peak beyond the band gap observed for both p- and n-type samples is considered to be an apparent one due to the bending of the sample in the highly absorbing region. The effect of the modulation frequency and the detector geometries are explained well by taking into account the sample bending and the pyroelectric effect.