The preparation of low-resistive p-ZnSe by closed Bridgman method

在室温下，ZnSe具有2.7 eV的直接带隙，是一种很有前途的蓝光二极管制备材料。近年来，对大面积、高质量的同质外延生长所需的锌硒衬底的需求十分迫切。为了满足上述要求，我们采用了由内PBN坩埚和外钼囊组成的封闭式双坩埚组件。确定了最佳生长条件：过热温度为76℃，生长界面温度梯度为30℃/cm，生长速度为3.6 mm/h，在此生长条件下，用多晶籽晶垂直布里奇曼法获得了直径为12 mm、长为55 mm的无孪晶的圆柱状黄色锌锌单晶。在解理的(110)晶面上进行的化学腐蚀表明，腐蚀坑密度(EPD)的平均值约为2.0×105 cm；四晶X射线衍射仪的摇摆曲线显示半高宽(FWHM)为19弧秒。在4.2K下的光致发光(PL)谱显示了可分辨的强束缚激子发射线和很弱的施主-受主对(DAP)发射带及其声子复制品。实验结果表明，用本方法生长的锌硒单晶具有很高的质量，并且通过改变组成和在原料中掺杂Sb或Bi的方法生长出了低阻的p型锌硒单晶。光致发光光谱显示出典型的高阻、低阻的p型发射。C-V特性表明，p型ZnSe的最高载流子浓度为5.5×10~(-3)cm~(-3)。此外，我们还尝试了用Pd金属制备欧姆电极。实验结果表明，Pd是一种很好的p-ZnSe电极材料。

ZnSe is a promising material for preparing blue light emitting diodes due to its suitable direct band gap of 2.7 eV at room temperature. Recently, there is an urgent demand for large area and high quality ZnSe substrates for homoepitaxial growth. In order to satisfy above requirement, we adopted a closed double-crucible assembly consisting of an inner pBN crucible and an outer molybdenum capsule. As an optimum growth condition, the superheating temperature of 76 ℃, the temperature gradient at the growth interface of 30 ℃/cm and growth rate of 3.6 mm/h have been determined.Using above growth conditions, the twin-free greenish yellow ZnSe single crystals of cylindrical shape with diameter of 12 mm and length of 55 mm have been obtained by the polycrystalline seeded vertical Bridgman method. Chemical etching on the cleaved (110) plane showed that the average value of etch pit density (EPD) is about 2.0×10^5 cm^<-2>. The rocking curves of 4-crystal X-ray diffraction showed the 19 arcsec in full-width at half-maximum (FWHM). The photoluminescence (PL) spectra at 4.2 K showed the resolved intensive bound exciton emission lines and the very weak donor-acceptor pair (DAP) emission bands and their phonon replicas. Above all results suggest that the ZnSe single crystals grown by the present method is of very high quality.Furthermore, the low resistivity p-type ZnSe single crystals have been grown by changing the compositions and doping Sb or Bi into starting materials. PL spectra show the typical emission of ZnSe single crystals with high-resistivity, low resistivity p-type. C-V characteristics showed that the highest carrier concentration in p-type ZnSe is 5.5×10^<16> cm^<-3>.By the way, we also tried to prepare the Ohmic electrodes by using Pd metal. The experimental results showed that Pd is a good candidate for the electrode material of p-ZnSe.