ABSTRACT High quality ZnS0.06Se0.94 epilayer which was lattice-matched to GaAs substrate has been prepared. The sulfur composition x was 0.06 has been determined by EPMA. The FWHM of X-ray diffraction was 187.2 arcsec. Its R-value was 5.191%. High quality ZnS0.06Se0.94:N epilayer which was lattice-matched to GaAs substrate has been prepared. The FWHM of X-ray diffraction was 169.2 arcsec. Its R-value was 3.521%. ITO film formed by thermal evaporated In-Sn alloy first, then annealing in O2 atmosphere. The conductivity and transparency of ITO have been trade-off at acceptable parameter. Because of the highest current in I-V characteristic in the structure of ITO/ZnS0.06Se0.94:N, we optimized the annealing temperature and time at 450¢J for 60min in O2 atmosphere. Because of the excellent transparency and conductivity in the structure of ITO/Glass, we optimized the annealing temperature and time at 650¢J for 60min in O2 atmosphere. The requirements for an excellent ohmic contact for ZnSe-based blue LED are: (1) transparent (2) low contact resistance (3) good for bonding (4) low melting point. For (1), Tin-doped indium oxide (ITO) is the only good choice. In this study, ITO/ZnS0.06Se0.94:Cl/ZnSe/ZnS0.06Se0.94:N/GaAs:Zn/Au-Zn double heterojunction (DH) structure has been prepared after annealing In-Sn/ZnS0.06Se0.94:Cl/ZnSe/ZnS0.06Se0.94:N/GaAs:Zn/Au-Zn in O2 atmosphere. I-V characteristic of DH junction structure shows a diode electric property.

ABSTRACT ZnSe-based materials have excellent characteristics for blue light emitting devices. So the substrates used for the growth of ZnSe-based alloys are considered from three points of (1) lattice match, (2) thermal match, and (3) interdiffusion. By replacing GaAs or GaP wafers by ZnSe substrates can avoid disadvantages of heteroepitaxy caused by lattice constant mismatch, by differential thermal expansion coefficients between substrate and epilayer. But the ZnSe substrate is cost too much. And it is not easy to achieve. So we choose the other way to get the substrate by Epitaxial Lift-Off (ELO). Another reason for this study is that the light extraction efficiency of these devices is limited by the optically absorbing GaAs substrate. So it can be improved by replacing GaAs with a new metal/glass substrate. The metallic interlayer can be used not only as an adhesive, but also as the reflective mirror to reflect light in the wafer-bonded LED structure. In this study, ZnSe-epliayer have been successfully lifted-off from GaAs by etching solution (NaOH(1M): H2O2(30%) = 4:1 or NH4OH(30%): H2O2(30%) = 9:1) and adhered it onto Indium/glass. From PL spectra, the PL intensity and broad band increases after ELO. The broad band can be decreased by surface trimming of citric etching solution (C6H8O7: H2O: H2O2 = 30g: 30ml: 10ml). This etching process is helpful in regrown ZnSe-epilayer. Regrowth of ZnSSe with [H2Se]/[H2S]¡×4 and II/IV=12.5, shows a NBE emission at 432nm with a FWHM of 26.6 meV at 77K PL spectrum. And the DAP is disappear after regrown. It means that the quality of ZnSe-epilayer becomes better after regrown.

GaN has the potential to revolutionize the high power electronics industry, enabling high voltage applications and better power conversion efficiency due to its intrinsic material properties and newly available high purity bulk substrates. However, unintentional impurity incorporation needs to be reduced. This reduction can be accomplished by reducing the source of contamination and exploration of extreme growth conditions which reduce the incorporation of these contaminants. Newly available bulk substrates with low threading dislocations allow for better study of material properties, as opposed to material whose properties are dominated by structural and chemical defects. In addition, very thick films can be grown without cracking due to exact lattice and thermal expansion coefficient match. Through chemical and electrical measurements, this work aims to find growth conditions which reduces contamination without a severe impact on growth rate, which is an important factor from an industry standpoint. The proposed thicknesses of these devices are on the order of one hundred microns and requires tight control of the intentional dopants. / Doctor of Philosophy / GaN is a compound semiconductor which has the potential to revolutionize the high power electronics industry, enabling new applications and energy savings due to its inherent material properties. However, material quality and purity requires improvement. This improvement can be accomplished by reducing contamination and growing under extreme conditions. Newly available bulk substrates with low defects allow for better study of material properties. In addition, very thick films can be grown without cracking on these substrates due to exact lattice and thermal expansion coefficient match. Through chemical and electrical measurements, this work aims to find optimal growth conditions for high purity GaN without a severe impact on growth rate, which is an important factor from an industry standpoint. The proposed thicknesses of these devices are on the order of one hundred microns and requires tight control of impurities.