Nomura Ichirou

Nitride has an attractive feature of bandgap engineering from ultraviolet to infrared. However, a lot of defects in nitride inhibit the feature. In this study, we demonstrated nitride nanocolumn on Si wafer that is expected realization of large-scale/low-cost devices. Furthermore, nanocolumn structure is expected to suppress propagation of dislocation. We employed a sputter-deposited AlN nucleation layer, because it is so difficult to grow nitride crystal on Si wafer. We successfully fabricated a single crystalline GaN nanocolumns array even on the sputter-deposited film containing high-density dislocations. Single-peak PL emission in wide visible range from integrated InGaN/GaN MQW, and control of PL peak wavelength by pre-patterning were also demonstrated.

MgZnCdSe, BeZnTe, and BeZnSeTe II-VI compound semiconductors grown on InP substrates are very attractive for middle visible range, especially green light emitting devices. We have developed these materials and emitting devices composed of BeZnSeTe active, MgSe/ZnCdSe superlattice (SL) n-cladding, and MgSeBeZnTe SL p-cladding layers. Long lifetime operations beyond 5000h were achieved for the devices, which shows a remarkable improvement of the aging characteristic of II-VI devices. We succeeded in photopumped green lasing at room temperature for the double heterostructures having a BeZnSeTe active layer to indicate a high potentiality of BeZnSeTe as an active layer of green laser diodes.

Novel II-VI compound materials such as MgZnCdSe, BeZnTe, and their related superlattices (SLs) grown on InP substrates were proposed for wide-range visible optical devices such as laser diodes (LDs) and light emitting diodes (LEDs).Visible LEDs consisting of ZnCdSe/BeZnTe SL active, MgSe/BeZnTe SL p-cladding, and MgSe/ZnCdSe SL n-cladding layers were fabricated to obtain wide-range visible electro luminescence (EL) emissions from 554 (yellow-green) to 644 nm (red). For yellow (575nm) LEDs, a long lifetime more than 3500 hours was demonstrated to show high reliability of the LEDs. LDs with ZnCdSe active layers were fabricated. Yellow-green lasing operations around 560 nm were successfully achieved under pulsed current injection at 77 K, for the first time.