Vapor Growth And Photoelectrical Properties Of ZnSe Bulk Single Crystals

As a direct wide-band-gap II-VI semiconductor, ZnSe single crystal has been identified as an important contender for the fabrication of blue-green light-diodes, nonlinear optic-electronic components and infrared devices. Because of its brilliant application prospects and the difficulties in single crystal growth, the growth technique and properties of ZnSe single crystals have attracted mach attention and have become the most active areas in ZnSe semiconductor research. In this thesis, we present our work on the optical and electronic property characterizations, as well as the growth methods. The synthesis mechanism of ZnSe polycrystals and the prepare of ZnSe nanocrystals, as an important relative research content, have also been studied.The crystals of ZnSe monocrystal grown via physical vapor transport(PVT) results higher cost and complicated procedures under congruent sublimation condition. Therefore, a new chemical vapor transport(CVT) method was designed to grow ZnSe crystals in our investigations. The compound (NH4)3ZnCl5 was employed as a transport agent in CVT method for the first time. This novel transport agent (NH4)3ZnCl5 possesses more advantages than lz, such as the higher thermostability, relatively lower pressure at room temperature, lower contamination level to ZnSe crystals. Moreover, NH3 gas from dissociation of (NH4)3ZnCl5, analogous to the inert gas, can adjust the growth rate of ZnSe and stabilize the vapor-solid interface, and avoid the difficulties of the non-emerging of Sen(n=2~8) in selenium vapor. Above all, (NH4)3ZnCl5 is a novel transport agent with comprehensive advantages.Based on the comprehensive analysis of the physical-chemical properties and the growth process of ZnSe single crystal, we paid more attention to two CVT methods with the same transport agents (NH4)3ZnCl5. One method is to grow ZnSe singlecrystal from polycrystals. As-grown ZnSe monocrystal, with 9 25mm in size, iscomposed of (111), (111) and two narrow (100), (001) faces. FWHM value of RO-XRD pattern of as-grown ZnSe crystal is determinated to be 24sec, and the average etch pit density is (5-7) 104cm-2. Non-emerging of SA(Self-Activated)luminescence and DAP(Donor-Acceptor Pair) emission in photoluminescence spectrum means that the ZnSe crystal grown by the first CVT method possesses high crystalline quality and high purity. The other CVT method is to grow ZnSe monocrystal from two elements zinc and selenium directly. The ZnSe monocrystalgrown by this method, with 8 7 0.5mm in size, exhibits only (111) face. FWHM value of its x-ray rocking curve is determinate to be 50sec, and the average etch pit density is (4~8) 104cm-2. The photoluminescence spectrum consists of a DAPemission and a broad SA luminescence band, and as-grown ZnSe crystal has high optical quality. The researching results show that a chemical transport agent introduced into our system can avoid the congruent sublimation condition and help to grow ZnSe crystal under relatively low temperature. This route will reduce the production cost of ZnSe single crystals.The study on the structure and micromorphology of two ZnSe monocrystal indicated that the growth mechanism of ZnSe monocrystal via vapor is two-dimension nucleation and growth, and (111) face is the mainly appearing face. The results provide an important experimental evidence for the growth theory of singular face.Ultrafast nonlinear optical properties of as-grown ZnSe single crystals were investigated by femtosecond pulses. Under femtosecond pulse excitation at SOOnm, SHG(Second-harmonic-generation) emission, the two-photon excited photolumines -cence and a broad emission can easily be detected at 402.0nm, 472.5nm and 500~700nm, respectively. The intensity of the broad emission at 500~700nm is rapidly decreasing with increasing temperature from 5K to 300K. This emission process can be described by two-component delay function and consist of two delay processes including a fast process and a delay one.Forward degenerate Four-Wave-Mixing experiment with...