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¥2,100,000 (Direct Cost : ¥2,100,000)
Fiscal Year 1996 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1995 : ¥1,600,000 (Direct Cost : ¥1,600,000)
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
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