A theoretical analysis has been carried out to compare the resonance condition in the asymmetric double-barrier structure with that in the symmetric triple-barrier one. It is. found that. the triple-barrier structure may be considered as two quasidouble-barrier structures whose resonance condition may decide the resonance levels in the triple-barrier structure. It is confirmed that two modes exist in the triple-barrier structure: one is "normal mode consisting of doublet and the other is degenerated mode of singlet. The critical condition between the two modes is given and its physical meaning is examined. Moreover, it is confirmed that both the normal mode and the degenerated mode exist also in symmetric n-fold barrier structures (n≥3).

A SiC light-activated Darlington heterojunction transistor is proposed for anti-EMI (electromagnetic interference) applications, in which a monolithically integrated SiCGe/SiC pn heterojunction photodiode is employed to produce a light-induced base current for triggering the transistor. Performance of the proposed light-activated power switch was simulated using MEDICI tools. Feasibility of the proposal is confirmed by its good light-activation characteristics obtained from the simulation. The simulation also demonstrates that good I-V characteristics with a light-independent turn-on voltage knee of about 5 V may be achievable to the light-activated power switch has.

SiCGe/SiC heterojunction structure is required in development of SiC optoelectronic devices and light-activated switching devices. We present in this paper a primary attempt to grow the ternary alloy SiCGe on SiC substrates under varied growth conditions in a conventional hot-wall CVD system. SiH4, GeH4 and C3H8 were employed as silicon, germanium and carbon sources, respectively. The samples were measured by means of SEM, XPS, XRD, optical absorption, etc. Two different growth modes i.e., island growth and porous growth were observed. It has been shown that germanium atoms can be effectively incorporated into the ternary alloys, which makes their optical gaps to be narrowed with increasing Ge content. However, incorporation of Ge induces a heavy lattice mismatch, which limits the film thickness by the formation of mismatch defects. It has been shown that use of a buffer layer can effectively improve the growth quality of the ternary alloy.

Optoelectronic characteristies of the SiCl-ZGeZ/SiC heterojunction photodiode are simulated using MEDICI after the theoretical investigation of key properties for SiCl-xGex. The calculations show that SiCl-xGex/SiC with x=0.3 may have a small lattice mismatch with 3C-SiC and a good response to the visible light and the near infrared light. The response spectrum of the SiCl-xGex/SiC heterojunction photodiode, which consists of a p-type SiCl-xGex absorption layer with a doping concentration of 1×1015cm-3 ,a thickness of 1.6μm and x=0.3, has a peak of 250mA/W at 0.52μm and the peak can even reach 102mA/W at 0.7μm.

Growth of SiCGe temary alloy on 6H-SiC in a conventional hot-wall CVD system was initially studied. SiH4, GeH4 and C3H8 were employed as silicon, germanium and carbon source, respectively, while H2 was employed as the carner gas. To reduce the heavy lattice mismatch between the film and the substrate, a 3C-SiC buffer layer was inserted between them in a CVD process. Optimizing the growth conditions was discussed. The samples were measured by means of SEM, SAXRD (Small Angle X-Ray Diffraction). It is shown that use of the 3C-SiC buffer layer is an effective way to improve quality of the ternary alloy.