The excitonic spin relaxation process in cubic GaN is observed by spin-dependent pump and probe reflectance measurements with subpicosecond time resolution. The spin polarization presents at temperatures lower than 100K. The spin relaxation times at 15–75K are found to be longer than 5ns and short spin relaxation times on the picosecond order are not present. Although these long spin relaxation times are in striking contrast to the subpicosecond spin relaxation of A-band free excitons in hexagonal GaN, they are consistent with the dependence that spin relaxation time becomes longer for wider-band gap zinc blende semiconductors.

The spin relaxation process of acceptor-bound excitons in wurtzite GaN is observed by spin-dependent pump and probe reflectance measurement with subpicosecond time resolution. The time evolutions measured at 15-50 K have a single exponential component corresponding to the electron spin relaxation time of 1.40-1.14 ps. The spin relaxation time is found to be proportional to T −0.175 , where T is the temperature. This weak temperature dependence indicates that the main spin relaxation mechanism is the Bir-Aronov-Pikus process ͓Sov. Phys. JETP 42, 705 ͑1976͔͒.

Cross‐sectional potential distribution in GaN‐based trench gate metal‐insulator‐semiconductor field‐effect transistors (MISFET) at off‐ and operating‐state has been investigated by using Kelvin‐probe force microscopy to clarify the actual operating situation of trench gate MISFET. The potential distribution reflecting the wafer structure, n/p/n–/n+, is observed as shown in the right figure. At the off‐state (the gate voltage is fixed to 0 V), it is found that the electric field at the internal p/n– interface become strong, on the contrary to that at top n/p interface is almost unchanged by the stepwise increase of the drain bias from 0 to 15 V. From the analysis of results obtained at operating state, we can confirm the situation how the channel forms by increasing the gate voltage. This information is useful for designing devices and improving their characteristics (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The spin relaxation process of acceptor-bound excitons in wurtzite GaN is observed by spin-dependent pump and probe reflectance measurement with subpicosecond time resolution. The time evolutions measured at 15-50 K have a single exponential component corresponding to the electron spin relaxation time of 1.40-1.14 ps. These spin relaxation times are slightly longer than those of the A-band free excitons of 0.47-0.25 ps in GaN at 150-225 K. The spin relaxation time is found to be proportional to T -0.175 , where T is the temperature. This weak temperature dependence indicates that the main spin relaxation mechanism is the Bir-Aronov-Pikus process. 1 Introduction Spin dynamics in semiconductors has been investigated with great interest, not only for fundamental physics but also for the application of spin-dependent optical nonlinearity such as spinmemory, spin-transistor and spin-switch devices. The picoseconds spin relaxation process in semiconductors became observable in the 1990s, using time-resolved spin-dependent pump and probe measurement [1] and time-resolved photoluminescence (PL) measurement with a streak camera system [2,3]. These experimental results revealed that the spin relaxation process decays rapidly in a few or a few ten picoseconds [1,4]. The application of this fast spin relaxation to ultrafast switching devices has been attempted [5][6][7]. In addition, because of the recent discovery of the considerable effect of spin polarization on vertical-cavity surface-emitting lasers [8], information on spin behavior has become important in the development of optical devices.The III-nitride-based semiconductors have been intensively investigated owing to strong interest in their application to optical devices such as the blue laser [9]. Investigations on spin dynamics in the GaN system are expected to yield information on the applicability of spin-related phenomena in the GaN system [10][11][12][13][14]. We have reported spin relaxation times of A-band free exciton in wurtzite GaN of 0.47-0.25 ps at 150-225K [11]. In cubic GaN, we have observed a long spin relaxation time of over 5 ns at 15 K [14]. The spin relaxation time is strongly affected by the band structure and the exciton state. In this paper, we report the observation of the spin relaxation process of acceptor-bound excitons in wurtzite GaN using time-resolved spin-dependent pump and probe reflectance measurement with subpicosecond time resolution.A shallow neutral acceptor-bound exciton (ABE) has a two-hole state derived from two holes in the topmost valence band [15]. Only one such state with J = 0 is allowed by the Pauli principle in wurtzite semiconductors. The additional electron in the ABE state then contributes to its unpaired spin; thus, this

SiC devices have the potential to reduce energy losses in high power applications. However SiC devices have yet to achieve ideal performance levels. This paper presents SiC diodes and MOSFETs with advanced trench structures. These devices succeeded in improving performance by reduction of the internal electric field. Trench Schottky diodes are able to reduce forward voltage drop and double-trench MOSFETs show extremely low on-resistance.