The Photoconductivity Of ZnS Under High Pressure

The Semiconductor Materials have got widespread application, which is important to the development of information industriesy. Among them, Electro-Optical Devices (semiconductor solar battery, solar cell, laser and so on) receive more and more attention for their good prospect. The electrical property is the foundation of semiconductor device.In this paper, with thin film deposition technology and the photoetching technology, we integrate micro electric circuit in the diamond anvil cell which can be used to study Direct current circuits. Electrical measurements under the high pressure has come true . The physical property is the collective behavior which the microparticle fellowship displays. High pressure, one extreme physical condition, can change the crystal structure effectively, influences the carrier transport in the crystal, causes the change of macroscopic conductance (resistance) finally. All of these days , semiconductor's properties under high pressure has been an important topic in the high pressure physics。ZnS is an intrinsic semiconductor, which has the good electro-optical performance, obtains the widespread application in optics and the photoelectric apparatus. This article takes the ZnS powder sample as the object of study, makes a systematic study of its property of high-pressure and illumination. The present paper mainly draws the following several conclusions:⑴Boundary structure: The grain boundary is the polysemiconductor's key character. The disorder and devious stoichiometric ratio of boundary structure (Dangling bonds) is responsible for acceptor interfacial state trap, which appears negativly after capturing electrons. The crystal grain interior, which approaches the crystal boundary at a distance, transforms into electron depletion layer .For this reason, Schottky barrier which is symmetrical to grain boundary has come into being . One hand, it reduces the free electron, on the other hand, it reduces mobility. Therefore, the polysemiconductor's conductance must be smaller than the same doping level of single crystal semiconductor .⑵T ransport mechanism: Polycrystalline's carrier transport is controlled by boundary potential barrier (double Schottky potential barrier). For ZnS sample, the conduction electron which only passes through the potential barrier (thermal excitation or tunneling) can form current. With the electric field, the potential barrier becomes no longer symmetrical. The experiment proves that the current transport is mainly desided by reverse bias depletion layer。(3)The influence of external voltage to grain boundary: The electrons by means of the heat emission or quantum tunneling can cross the potential barrier to carry on the transport. Heat emission current is influeced by the temperature, has nothing to do with the barrier width. The quantum tunneling probability is concern with the barrier width. Under the low voltage, depletion-layer width is big, the tunneling electron may neglect, the thermal excitation electron occupies the whip hand. The potential barrier acts as high resistance for the hindrance to carriers, the macroscopic electric current is very small. Increases the external voltage, the upper of depletion layer is narrow , the tunneling electron surpasses the thermal excitation electron to become the main transport mechanism.⑷Influence of illumination: When X light illuminates the sample, the sample produces the additional carrier. The light-generated electron-hole pairs are separated by the electric field, enter the grain boundary and the crystal separately. A part of hole are recombinate with interface traps。With the effective electric-charge density'reduction, the potential barrier reduces, the scattering of carrier through grain boundary is weaken. As the carrier concentration and mobility increases, conductance increases. The illumination increaseds the conductance.⑸Persistent photoconductivity: Get rid of illumination, the conductance must pass through certain time to restore to the dark conductance. Light-generated electron-hole's recombination take place in grain, concerns with the shallow donor level. The other are trapped in the grain boundary, because the limit of the potential barrier, the recombination must be slower compared to volume recombination。We may see from the above analysis, the grain boundary's influence mainly manifests in the grain boundary potential barrier and interfacial state. The illumination and the voltage may reduce the barrier height, the thermal excitation current increase. The electric field may also make depletion layer width get narrow, tunneling electron become the domaint. A fraction of interface States are the recombination center for the traps. The developed country has given the enormous attention to the applicition of the grain boundary's development. The research of semiconductor's interfacial effect and corresponding theory have the very vital practical significance to the optimizition of component performance and explorition of the new component...