野村 一郎

Conduction band discontinuity (ΔEc) of MgSe/ZnCdSe heterojunctions were evaluated using n–i–n diodes consisting of an undoped i-MgSe layer sandwiched by n-doped ZnCdSe layers. The n–i–n diodes were fabricated on InP substrates by molecular beam epitaxy. Injection current density versus applied voltage (J–V) characteristics of the n–i–n diodes were measured at 77 K and room temperature. In addition, the theoretical J–V characteristics of the n–i–n diode were calculated while varying ΔEc. By fitting the theoretical data to the experimental data, ΔEc was estimated to be 1.2 eV from the result at 77 K. This value is similar to the ΔEc estimated from the literature.

The application of indium tin oxide (ITO) as the p-cladding layer of II-VI compound semiconductor laser diodes (LDs) on InP substrates was investigated. The waveguide analysis of the LD structures revealed that the optical confinement effect around the active layer was obviously improved by changing the p-cladding layer from the conventional MgSe/BeZnTe superlattice to ITO. For example, the estimated optical confinement factors were 0.15 and 0.27 for the conventional and ITO LD structure, respectively, when the emission wavelength was 580 nm. In addition, we investigated optimum LD structures, considering the optical and carrier confinements at the active layer. In experiments, light emitting devices with an ITO layer were fabricated on InP substrates via molecular beam epitaxy and radio-frequency (RF) magnetron sputtering. Yellow emissions at 582 nm were observed by current injections at room temperature. These results indicate that ITO is a promising p-cladding layer material for II-VI LDs on InP substrates. (C) 2016 WILEY-VCH Verlag GmbH & Co.

II-VI-compound-semiconductor laser diode (LD) structures on InP substrates were investigated using device simulations and waveguide analysis. Our simulations showed that electron injection from the n-cladding into the active layer is hindered by the n-side barrier layer between the n-cladding and active layer. Consequently, holes are not injected into the active layer but instead leak to the n-side layers. It was shown that carrier injection efficiency can be improved by removing the n-barrier. On the contrary, no large differences were observed between the optical confinement factors of the LD structures with and without the n-barrier layer. In ex-periments, we have fabricated the LD structures with and without the n-barrier layer on InP substrates using molecular beam epitaxy. The turn-on voltage of the device without the n-barrier was smaller than that for the device with the n-barrier by about 5 V. Spontaneous orange emissions around 603 nm were observed for the devices without the n-barrier. In contrast, no emission was observed for the devices with the n-barrier. These results prove that the carrier injection into the active layer is enhanced by the removal of the n-barrier, leading to improved the device performances. (C) 2016 WILEY-VCH Verlag GmbH & Co.

N-doped p-type ZnTe and ZnSeTe contact layers were investigated to evaluate which is more suitable for use in II-VI compound semiconductor optical devices on InP substrates. Contact resistances (R-c) between the contact layers and several electrode materials (Pd/Pt/Au, Pd/Au, and Au) were measured by the circular transmission line model (c-TLM) method using p-n diode samples grown on InP substrates by molecular beam epitaxy (MBE). The lowest R-c (6.5 x 10(-5) Omega cm(2)) was obtained in the case of the ZuTe contact and Pd/Pt/Au electrode combination, which proves that the combination is suitable for obtaining low R-c. Yellow light-emitting diode devices with a ZnTe and ZnSeTe p-contact layer were fabricated by MBE to investigate the effect of different contact layers. The devices were characterized under direct current injections at room temperature. Yellow emission at around 600 urn was observed for each device. Higher emission intensity and lower slope resistance were obtained for the device with the ZuTe contact layer and Pd/Pt/Au electrode compared with other devices. These device performances are ascribed to the low R-c of the ZnTe contact and Pd/Pt/Au electrode combination. (C) 2015 Elsevier B.V. All rights reserved.