Dynamic behaviors of gas/plasma mixture generated by microwave discharge jet at atmospheric pressure have been investigated in terms of the effects of working gas dynamics on the discharge characteristics, focusing on the following four points: formation of discharge jet at the ignition phase, growing speed of plasma plume in relation to gas flow rate, acceleration and deceleration of upward movement of plasma plume, and decay process of plasma column at turn-off of microwave power. Four stages are identified at the discharge ignition. The acceleration coming from buoyancy effect and the deceleration due to gas flow turbulence have been found. The decay speed of plasma column at a power shut-off is found to be influenced by the gas flow turbulence and the recombination rate.

A high-field operation of p+–n structure blue-ultraviolet photodetectors has been studied using ZnSe-based II–VI wide-band-gap compound semiconductors grown by molecular-beam epitaxy (MBE). With an improved crystal quality on macrodefects (dislocations and stacking faults) during an initial MBE growth as well as an optimized device structure including a complete superlattice ohmic-contact layer, a stable high electric-field operation up to 8×105 V/cm is established. It is demonstrated that the p+–n ZnSe photodiodes have shown a stable avalanche-photodiode operation with a large avalanche gain of G=60 in the blue-ultraviolet region at room temperature.

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This paper presents slow-mode degradation mechanism of ZnSe-based white LEDs. A systematic study has been made from a viewpoint of microscopic point defect reaction such as generation and migration in both device active layer (ZnCdSe/ZnSe MQW) and p-type ZnMgSSe cladding layer utilizing DLTS/ ICTS, SSRM (scanning spreading resistance microscope), and EL (electroluminescence)-imaging techniques, coupled with device aging experiments. We have found two different degradation stages (1st and 2nd stages) in the slow-mode degradation, which are caused by quite different microscopic point defect species. The 1st stage is induced by the long-diffusion of H0-center (nitrogen-complex deep hole trap in p-cladding layer), forming high-density dark-spots in the MQW active layer. This active center is generated only in the stress-stimulated condition such as thermal or device fabrication process. After controlling the initial concentration of the H0 center, we have observed no detectable new dark-spots during device operation, leading to fairly long device-lifetime (~1000 h). This 2nd stage has appeared as a carrier (hole) reduction in the p-type cladding layer. This final degradation stage is found to take place by an increase of shallow compensating donor-like centers in p-type cladding layer (ZnMgSSe). Based on these insights on the microscopic point defect reaction, we have developed (new) double cladding i-ZnMgBeSe/ p-ZnMgSSe white-LEDs, which has exhibited long device lifetime of over 10 000 h.