Shigeru Shigetomi

Optical and electrical properties of layer semiconductor p‐GaSe doped with Zn

Zinc (Zn) is doped into GaSe single crystals grown by the Bridgman technique in a wide range from 0.005 to 0.5 at. % to the stoichiometric melt. Radiative recombination mechanisms have been investigated by using photoluminescence (PL) measurements. The PL spectra in Zn‐doped samples at 77 K are dominated by three emission bands at 1.75, 1.63, and 1.27 eV. The 1.63 and 1.27 eV emission bands are enhanced with the increase in the amount of Zn. In addition to the results of Hall effect measurements, it is found that the 1.63 and 1.27 eV emission bands are associated with the acceptor levels at 0.12 and 0.3 eV above the valence band, respectively. For the 1.27 eV emission band, the temperature dependences of the PL intensity, peak energy, and half‐width are characterized by the configurational coordinate model.

Electrical and photovoltaic properties of Cu-doped p-GaSe/n-InSe heterojunction

GaSe(Cu)/InSe heterojunctions have been formed by bringing the cleavage surface of undoped n-InSe and Cu-doped p-GaSe into direct contact. Transport and phototransport properties are studied by the measurements of capacitance–voltage, current–voltage, and the spectral response of short-circuit current. Moreover, the efficiency parameters under illumination are estimated by using the open-circuit voltage and short-circuit current. These characteristics of GaSe(Cu)/InSe heterojunctions are compared with those of GaSe(Un)/InSe heterojunctions fabricated by undoped p-GaSe and n-InSe. The series resistance of GaSe(Cu)/InSe heterojunctions is found, the value of which is about 103 times lower than the corresponding value of GaSe(Un)/InSe heterojunctions. A short-circuit current density of 9.0 mA/cm2 and an open-circuit voltage of 0.42 V on GaSe(Cu)/InSe heterojunctions are obtained under illumination of 120 mW/cm2 of a halogen lamp. The short-circuit current of GaSe(Cu)/InSe heterojunctions is about one order o...

Near Band Edge Photoacoustic Spectra of p-Si Single Crystals

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.

A theoretical explanation for the red energy shift of a newly discovered, exclusively acceptor‐associated emission in GaAs

Radiative mechanism of a newly discovered near‐band‐edge emission, [g‐g], exclusively associated with acceptor impurities in GaAs, was theoretically discussed. Since the emission energy of [g‐g] for the lowest acceptor concentration limit is nearly identical to that of the excited state of the acceptor impurities and it shows a noticeable shift towards lower‐energy levels with increasing acceptor concentration, it was suggested that the energy of [g‐g] corresponds to the 2pσ bond state of the acceptor‐acceptor pair formed by the overlapping of the 2p excited state. The calculated energy of the 2pσ bond as a function of the distance between the acceptor‐acceptor pair shows good agreement with the experimentally obtained value of [g‐g] in Mg‐doped GaAs grown by molecular‐beam epitaxy (MBE). From a comparison of binding energies in the acceptor‐doped GaAs samples prepared by ion implantation (Zn+ or Mg+) and by MBE, the activation ratio of the implanted atoms was estimated.

Photoluminescence spectra of p-GaSe doped with Cd

Impurity levels in Cd‐doped GaSe have been studied by using photoluminescence (PL) measurements. The PL spectra at 77 K are dominated by three new emission bands at 1.95, 1.75, and 1.62 eV. The PL intensity and the peak energy of the 1.95 and 1.62 eV emission bands are measured as a function of the temperature. It is shown that the 1.95 eV emission band is due to the transition between the conduction band and the acceptor level at 0.18 eV above the valence band. The 1.62 eV emission band is caused by the transition from the donor level at 0.37 eV below the conduction band to the acceptor level at 0.13 eV above the valence band. The PL intensity increases with increasing Cd concentration.

INFLUENCE OF THE IMPLANTATION OF C+ IONS ON PHOTOLUMINESCENCE AND ELECTRICAL PROPERTIES OF GAAS

Ion implantation of carbon (C) into extremely pure GaAs grown by molecular‐ beam epitaxy is carried out over a wide range of C atomic concentrations [C], from 1×1016 to 5×1019 cm−3. The impurity levels in the implanted layer are investigated by using photoluminescence (PL) and Hall‐effect measurements. Below the well‐defined exciton luminescence lines, one broad emission band, namely [g‐g], is found to be exclusively attributable to acceptor impurities and is dominant for [C] lower than 3×1017 cm−3. However, a decrease of its intensity and a ‘‘locking’’ of its emission energy shift is observed for [C] higher than this value. A carrier transport mechanism is found to be relevant to the C acceptor level for C atoms at As sites, and deep acceptors caused by residual radiation defects. The concentration of substitutional C atoms is nearly coincident with [C] up to 1×1017 cm−3, but the activation efficiency for [C]=1×1018 cm−3 decreases by about 13%. The decrease of overall PL intensity and the locking of the ...

Impurity levels in layer semiconductor p‐GaSe doped with Mn

The impurity levels in Mn‐doped GaSe have been investigated by using photoluminescence (PL), Hall effect (HE), and deep‐level transient spectroscopy (DLTS) measurements. The emission band at 1.82 eV is observed on the PL spectra of the samples doped with Mn of wide range from 0.01 to 1.0 at. %. We find, from the temperature dependences of PL intensity and peak energy, that the 1.82 eV emission band is due to the transition between the conduction band and the acceptor level at 0.32 eV above the valence band. The acceptor level located at about 0.34 eV above the valence band is detected by using HE and DLTS measurements. The dominant acceptor level in the carrier transport shows almost the same position as that of the radiative recombination center. This acceptor level is probably associated with the defects formed by Mn atoms in the interlayer or interstices.

As4 to Ga flux ratio dependence of the optical and electrical properties of Ge‐doped GaAs grown by molecular‐beam epitaxy

A drastic change of the conduction type from p to n with an increase of the As4 to Ga flux ratio, γ, was observed for the first time in the photoluminescence spectra of amphoteric impurity (Ge)‐doped GaAs made by molecular‐beam epitaxy. The sample with the lowest γ (γ=1.0) presented a purely p‐type emission associated with pairs between the excited states of acceptors. The sample with the highest γ (γ=10.6) indicated a totally n‐type emission reflecting an increase of quasi Fermi energy. Results show that by precisely controlling the flux ratio, γ, one can reliably make use of substantially amphoteric atoms of Ge both as p‐ and n‐type impurities for the fabrication of GaAs by molecular‐beam epitaxy.

Zn‐induced impurity levels in layer semiconductor InSe

The impurity levels in Zn‐doped InSe have been investigated by photoluminescence (PL), Hall effect (HE), and deep‐level transient spectroscopy (DLTS). Previous analysis by PL spectra shows that the radiative transition is dominated by donor‐Zn acceptor pairs. In the present work, a search was made for the deep acceptor level using the combined data from HE and DLTS measurements. We find that the deep acceptor level, which is associated with defects or defect complexes formed by Zn atoms in the interlayer, is located about 0.6 eV above the valence band.

Temperature dependence of photoluminescence of layer semiconductor p-GaTe

The photoluminescence (PL) spectra of undoped p-GaTe at 97 K are dominated by two emission bands at 1.76 and 1.59 eV. For the 1.76 eV emission band, the behavior of the peak energy and full-width at half-maximum as a function of temperature shows the characteristics of the recombination mechanism for the free exciton. We find, from the temperature dependence of the PL intensity of the 1.59 eV emission band, that the band is caused by the transition from the donor level to the acceptor level located at 0.15 eV above the valence band.