Electronic Engineering Course

Towada, Japan

Electronic Engineering Course

Towada, Japan

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Onodera C.,Electronic Engineering Course
Journal of Physical Studies | Year: 2011

We investigated the effect of H 2 heat treatment on CdTe films grown on GaAs substrates by using photoluminescence (PL) and reflectance spectra. We observed the changes in heavy- and light-hole free exciton (FE) emissions and reflectance spectra with heat-treatment temperature. The energy separation between heavy-hole and light-hole FE lines calculated using the bimetallic strip model is in good agreement (4.08 meV) with that estimated from the peak energies of the heavy- and light-hole FE lines (4.0 meV). By Lorentzian deconvolution of the heavy-hole and light-hole FE lines, their widths decrease with increasing H 2 heat treatment temperature. By fitting the theoretical reflectance spectra to the measured reflectance spectra, the associated broadenings of light-hole FEs decrease with increasing H 2 heat treatment temperature. The observations suggested that the crystallinity of CdTe films is improved by H 2 heat treatment.


We study the effects of exciton-longitudinal optical phonon interaction on the exciton binding energies in ZnS/MgxBeyZn 1-x-yS single quantum wells. The heavy- and light-hole exciton binding energies increase to the exciton-logitudinal optical phonon interaction. The increase in the maximum heavy-hole (light-hole) exciton binding energy for x = 0.74 is 68.3 meV (55.0 meV). In narrow ZnS/MgxBe yZn1-x-yS single quantum wells SQWs, the heavy- and light-hole exciton binding energies exceed the longitudinal optical phonon energy of ZnS when x ≥ 0.1.


Onodera C.,Electronic Engineering Course
Journal of Physical Studies | Year: 2010

Binding energies of heavy- and light-hole excitons in CdS/MgS single quantum wells (SQWs) are calculated by considering the effect of dielectric confinement (image charge effect). The increase in maximum heavy-hole (light-hole) exciton binding energy calculated by considering the image charge effect is 7.7 meV (5.9 meV). When the well width of the CdS/MgS SQWs is in the range of 0.5 nm-4.0 nm the heavy- and light-hole exciton binding energies calculated by considering the image charge effect are larger than the longitudinal optical phonon energy of CdS.


Onodera C.,Electronic Engineering Course | Shoji T.,Tohoku Institute of Technology | Taguchi T.,Yamaguchi University
Optical Review | Year: 2010

We calculate optical gain coefficient and threshold current density in ZnS/MgBeZnS quantum wells (QWs) because ZnS/MgBeZnS QWs are useful for the fabrication of an ultraviolet laser on zinc-blende substrates. The threshold current density in a ZnS/MgBeZnS QW laser diode (LD) with a 10 nm ZnS active layer is calculated to be 1.63 kA/cm2. By comparing the measured Jth in a CdZnSe/ZnSSe/ZnMgSSe QW LD with that calculated by us, it is expected that the threshold current density in ZnS/MgBeZnS QW LDs measured by experiment is larger than that calculated by our calculation method. © 2010 The Optical Society of Japan.


Onodera C.,Electronic Engineering Course | Taguchi T.,Yamaguchi University
Japanese Journal of Applied Physics | Year: 2010

We performed photoluminescence (PL) and reflectance characterization of CdTe films on GaAs substrates. Separate emission peaks for heavy-and light-hole free excitons due to induced compressive strain were observed. The strain in a CdTe film is estimated to be ε = -5.28 × 10-4. By analyzing the PL and reflectance spectra, both heavy- and light-hole free exciton binding energies are estimated to be 9.9 meV. By analyzing the energy separation between the heavy- and light-hole free exciton reflectance dips, the magnitude of the residual compressive strain is determined to be homogeneously distributed within a CdTe film. From the CdTe film thickness dependence of heavy- and light-hole free exciton linewidths, the CdTe film quality is observed to become poor with decreasing CdTe film thickness. © 2010 The Japan Society of Applied Physics.


Onodera C.,Electronic Engineering Course
e-Journal of Surface Science and Nanotechnology | Year: 2010

We calculate the binding energies of heavy- and light-hole excitons in ZnS/MgxZn1-xS single quantum wells (SQWs) as functions of the well width by using a variational method. We take into account the effect of the mismatch between the dielectric constants of the well and the barriers (dielectric mismatch effect) in our calculation. The increases in the heavy- and light-hole exciton binding energies in ZnS/MgxZn1-xS SQWs for a Mg content (x) of 1.0 are 58.9 meV and 60.2 meV, respectively. In the case of narrow wells, the heavy- and light-hole exciton binding energies calculated by considering the dielectric mismatch effect exceed the longitudinal optical phonon energy of ZnS when x ≥ 0.3. © 2010 The Surface Science Society of Japan.


Onodera C.,Electronic Engineering Course
e-Journal of Surface Science and Nanotechnology | Year: 2010

We study the effect of the exciton-longitudinal optical (LO) phonon interaction on the exciton binding energies in CdxZn 1-xS/ZnS single quantum wells (SQWs) for the Cd alloy content (x) range 0.1-0.3. The heavy- and light-hole exciton binding energies increase with the exciton-LO phonon interaction. The increase in the maximum heavy-hole (light-hole) exciton binding energy for x = 0.3 is 9.1 meV (4.9 meV). In narrow CdxZn1-xS/ZnS SQWs, the heavy-hole exciton binding energy calculated by taking into account the exciton-LO phonon interaction for values of x in the range 0.1-0.3 exceed the LO phonon energy of CdxZn 1-xS. © 2010 The Surface Science Society of Japan.


Onodera C.,Electronic Engineering Course
e-Journal of Surface Science and Nanotechnology | Year: 2011

Exciton binding energies in ZnSSe/MgSSe single quantum wells (SQWs) are calculated to study their exciton properties in detail. The heavy-hole exciton binding energies are larger than the light-hole exciton binding energies in narrow wells because the degree of confinement of the heavy-hole excitons is larger than that of the light-hole excitons in these SQWs. The heavy-hole exciton binding and heavy-hole excitonic transition energies calculated for ZnSSe/MgSSe SQWs are comparable to those measured for ZnSe/MgS quantum wells. © 2011 The Surface Science Society of Japan.


Onodera T.,Tohoku Institute of Technology | Hitomi K.,Tohoku University | Onodera C.,Electronic Engineering Course | Shoji T.,Tohoku Institute of Technology | Mochizuki K.,Ishinomaki Senshu University
IEEE Transactions on Nuclear Science | Year: 2012

Thallium bromide chloride (TlBr x Cl 1-x) crystals have been evaluated as a material used for fabrication of room temperature radiation detectors. In this study, TlBr x Cl 1-x crystals with various chlorine (Cl) concentrations were grown by the travelling molten zone method and the detectors were fabricated from the crystals. The optical properties of the crystals were evaluated by measuring the transmittances. The charge transport properties were characterized by the Hecht analysis. The band gap energy of the crystals proportionally increased with Cl concentration. Mobility-lifetime products (μm τ) of the crystals decreased with increasing Cl concentration. © 2012 IEEE.


We study the effects of the exciton-longitudinal optical (LO) phonon interaction and quantum confinement on the exciton binding energies in ZnS 1-x Se x/ZnS single quantum wells (SQWs) for an Se alloy content (x) range of 0.1-0.3. In narrow ZnS 1-x Se x/ZnS SQWs, the heavy-hole (lighthole) exciton binding energy calculated by taking into account the exciton-LO phonon interaction for values of x in the range of 0.2-0.3 (0.3) exceeds the LO phonon energy of ZnS 1-x Se x. The difference between the maximum heavy-hole (light-hole) exciton binding energy for x = 0.3 and the LO phonon energy is less than 1.5 meV (1.0 meV). This SQW shows a weak quantum confinement due to a small conduction-band offset.

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