Low Pressure Vapor Phase Growth and Control of Electrical and Optical Properties of Zinc Selenide Single Crystalline Thin Films

采用低压气相外延（LPVPE）技术在砷化镓（GaAs）衬底上生长了硒化锌（ZnSe）单晶薄膜，其中锌和硒的蒸气被提供到压力为10^<-6>-10^<-1> Torr的氢气气氛中。利用氢射频等离子体在外延生长前对衬底表面进行清洗，获得了高重复性的生长实验。通过对生长过程中VI/II比的精确控制，生长出了具有以自由激子发射为主的低温光致发光光谱的高纯度未掺杂ZnSe层。在0.1 Torr下生长的未掺杂ZnSe层具有较高的电阻率。In掺杂增加了载流子浓度，并控制在10^<16>-10^<18> cm^<-3>的范围内。当生长压力为10^<-4> Torr时，未掺杂层的电阻率低至几厘米。层电阻率的生长压力依赖性表明，补偿浅层残余供体的深部能级密度随生长压力的变化而变化。室温载流子浓度为5x10^<15> cm^<-3>的2n掺杂层，其低温电子迁移率高于800 cm^2/v.sec。高迁移率表明残留杂质密度低。当NH_3气体进入生长腔时，在2.793 eV处发现了一条新的发射线，这是由于激发结合在一个浅层受体上的重组而产生的，并且随着NH_3浓度的增加，发射强度增加。随着VI/II比的增大，受体结合激子发射强度减小，确定了发射是由Se位点的N受体引起的。

Single crystalline thin films of zinc selenide (ZnSe) have been grown on GaAs substrates by using low pressure vapor phase epitaxy (LPVPE) technique, in which zinc and selenium vapors are supplied into hydrogen atmosphere with pressure of 10^<-6>-10^<-1> Torr. A high reproducibility in growth experiment was attained by utlizing the hydrogen RF plasma cleaning of substrate surface just before the epitaxial growth. The VI/II ratio during the growth was precisely controlled and high-purity undoped ZnSe layers, which exhibit low-temperature photoluminescence spectra dominated by the free exciton emission, were grown.Undoped ZnSe layers grown at 0.1 Torr were of high resistivities. The carrier concentration was increased by In doping and controlled in the range of 10^<16>-10^<18> cm^<-3>. When the growth pressure was 10^<-4> Torr, undoped layers showed low resistivities of several .cm. The growth pressure dependence of the layer resistivity indicates that the density of deep levels compensating the residual shallow donors varies with the growth pressure. An 2n-doped layer with room-temperature carrier concentration of 5x10^<15> cm^<-3> had a low-temperature electron mobility higher than 800 cm^2/v.sec. The high mobility indicates low densities of residual impurities. When NH_3 gas was introduced into the growth chamber, a new emission line due to recombination of excition bound to a shallow acceptor was observed at 2.793 eV, and the emission increased in intensity as the concentration of NH_3 was increased. The acceptor bound exciton emission intersity decreased with increasing the VI/II ratio, which ascertained that the emission was due to N acceptor at Se site.