Tham khảo tài liệu 'optoelectronics materials and techniques part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 170 Optoelectronics - Materials and Techniques contains an interfacial layer on the silicon surface. However in the present work we could not observe any interfacial layer on the silicon surface . Figure 5 shows the high-resolution transmission electron microscopy HRTEM image of a ZnSe Si heterostructures which reveals a clear interface between substrate silicon and overlayer zinc selenide layer . The main reason is the existence of a laterally varying potential barrier height caused by a non-uniform interface. D -2 -1 0 1 2 V volt Fig. 4. Forward and reverse current versus voltage characteristics of ZnSe Au Schottky diode. The inset of shows the plot of voltage versus LnI. Reprinted with permission from Venkatachalam et al. 2006 . Copyright @ IOP Publishing Ltd 2006 . The reverse bias characteristics would be controlled by the generation-recombination and band-to- band tunneling mechanisms at small up to V and large bias respectively which might be the reason for a small kink at V Chiang Bedair 1985 . The plot between the measured values of capacitance and voltage for ZnSe p-Si diodes is shown in Fig. 6a. We obtained a straight line by plotting a curve between 1 C2 versus V which implies a similar behaviour for an abrupt heterojunction Khlyap Andrukhiv 1999 . The intercept of this plot at 1 C2 0 corresponds to the built-in potential Vbi and is found to be V. The value of barrier height Singh et al. 1993 Pfister et al. 1977 can be calculated from the measured value of Vbị. 2 TZ kT fan - Vbi Vn q where Vn kT q. Ln Nv NA k is the Boltzmann constant T is the temperature q is the charge of the electron Nv is the density of states in the valence band and NA is the effective carrier concentration. From the slope of the 1 C 2 versus voltage plot the value of effective carrier concentration is calculated as X 1019 m2 F 2 V. The calculated values of barrier height and .
