Low Temperature Growth and Conductivity Control of High Quality ZnS Layrs Grown by Using High TemperatureE Molecular Beams

本研究采用分子束外延(MBE)方法在不同取向的GaAs(001)和非取向的GaAs(001)衬底上生长了ZnS/GaAs层和ZnSe/GaAs层，并用反射高能电子衍射仪(RHEED)研究了它们的生长过程，研究了外延层的生长速率和光学性质。本实验中使用的分子束是从传统K细胞出口处加装额外加热器的流出室中排出的后热分子束，作为P型受主掺杂，Li束以元素Li提供到传统K细胞的生长表面。我们发现，在分子束外延生长过程中和生长后，弯曲条纹都出现在RHEED图案中。弯曲条纹的产生归因于与Li相关的一维晶格，即Li原子被表面平台B阶边的Se原子选择性俘获。此外，如果在GaAs(001)面上添加Li原子，Layr生长速率会降低，…此外，如果Li束流超过一定的量，则不会发生外延生长。这意味着很难生长出足够厚度的高掺杂Li层。生长速率降低的原因是Li原子控制的B型阻碍了这些台阶边缘的层状生长。然而，我们发现，如果使用错位的砷化镓衬底(15ﾟ关断)，生长速率不会降低。在Li掺杂的硫化锌和硒锌薄膜中，Li受主激子(I_1)的发射、FA和DAP发射占据了光致发光谱，其他发射很弱，这表明外延层是高纯度的。FA发射占主导地位，意味着间隙Li等施主杂质的浓度极低。因此，我们可以说，用后加热分子束生长分子束外延层是生长锂掺杂外延层的一种有效方法。我们还在未掺杂的ZnSe/GaAs的光致发光光谱中发现了令人费解的现象，即在光致发光测量过程中发射强度增加。我们认为，IV发射的发射中心是由Se空位和光激发载流子形成的。较少

In this study, , ZnS/GaAs and ZnSe/GaAs epitaxial layrs were grown on GaAs (001) and misoriented GaAs (001) substrates by a molecular beam epitaxy (MBE), and their growth process were studied by means of a reflection high energy electron diffracti on (RHEED) , and the growth rate of epitaxial layr and the optical property were investigated. The molecular beams used in present experiment are post-heated molecular beams exhausted from the effusion cell equipped with extra heater at the outlet of conventional K cell.As P-type acceptor dopant, Li beam is supplied onto the growing surface form conventional K cell using elemental Li. We found that the curved streaks appear in the RHEED pattern during and after MBE growth. The origin of curved streaks are attributed to the one-dimensional Li-related lattice, ie., Li atoms are selectively captured by Se atoms at B-step edge of surface terrace. Furthermore, if Li atoms are suppled on GaAs (001) -just surface, the layr growth rate decreases and … More if Li beam flux exceeds a certain amount, no epitaxial growth takes places. This means that the growth of Li highly doped layr with sufficient thickness is difficult. The reason of growth rate reduction is attributed to the B-type teminated with Li atoms obtacle the layrer growth from these step edges. However, we found that the growth rate reduction does not occur, if the misoriented GaAs substrates (15ﾟoff) are used.In Li-doped ZnS and ZnSe layrs, the emission from Li-acceptor bound exciton (I_1) , FA and DAP emissions dominate the PL sectrum and other emissions are very weak, which denotes the epitaxial layrs are high Purity. The dominace of FA emission means that the concentration of donor-like impurities such as interstitial Li is extremely low. Thus, we can say that the MBE growth using post-heated molecular beams are an effective method to grow Li-doped epitaxial layrs.We also found puzzuling behvior of Iv emiison obserev in the PL spectra of undoped-ZnSe/GaAs, i.e., the emission intensity increases during PL measurement. We concluded that the emission center for Iv emission is formed by Se vacancy and photo-excited carriers. Less