Photoluminescence Studies of Aluminum

Available from UMI in association with The British Library. Various studies have been performed on undoped and heavily doped Al_{x}Ga _{1-x}As epitaxial layers with 0.01 <= x <= 0.87 grown on (100) Si-doped GaAs substrates by LPE, MOCVD, and MBE techniques. Hall effect and resistivity measurements show room temperature free-carrier concentrations from 1.06 times 10^{17 } to 4.1 times 10 ^{18} cm^{ -3}. Photoluminescence measurements were made on all of the samples at temperatures from 8 to 400K. The design and construction of apparatus for photoluminescence measurements over a wide temperature range is discussed. The apparatus was designed so that electrical measurements could also be made, with little or no rearrangement of the sample or the apparatus between the different types of study. In the case of the undoped LPE epitaxial samples, the low temperature spectra consist of a narrow band (peak B) and a less intense band (peak A), which are identified as due to acceptor free to bound and band to band recombination respectively. The photoluminescence spectra of heavily Zn-doped Al_{x}Ga _{1-x}As grown by MOCVD exhibits near band-edge emission bands and low energy broad bands. From the luminescence behaviour we suggest that (Zn _{Ga}-V_{As }) or (Zn_{III} -V_{III}) complexes are responsible for the broad bands, although the details remain unknown. The low temperature photoluminescence spectra of heavily Be-doped Al_{x}Ga _{1-x}As grown by MBE exhibit two emission bands peaking at ~1.96eV and ~1.49eV respectively. As the temperature increases, a broad band about 160meV below the edge emission starts to appear, and analysis based on temperature and excitation-intensity dependence suggests that this is due to a vacancy-dopant complex, which acts as a nonradiative center at room temperature as the band completely disappears at room temperature. The results of a systematic photoluminescence study of AR film-(p)Al_{x}Ga _{1-x}As-(p)GaAs-(n)GaAs solar cells are reported. A photoluminescence and step etching technique was developed for accurate evaluation of the internal efficiency and of the effects of each layer in the solar cell. The improved PL efficiencies compared to conventional homojunction GaAs cells are attributed to the reduction of surface recombination losses resulting from the presence of the heavily doped Al_ {x}Ga_{1-x}As window layer, and evaluation of the surface recombination velocity is attempted for the range 10 to 200K.