R. Schwabe

Reduced EL2 concentration in MOCVD GaAs by addition of NH3 during growth

Abstract The admixture of ammonia during MOCVD growth of GaAs results in a considerable decrease of the EL2 concentration in the epitaxial layers. EL2 concentrations as low as 1012 cm-3 have been obtained with n300 about 1015 cm-3 and μ300 about 6900 cm2/V·s. Luminescence measurements show near gap emission lines having a very small half width (0.3 meV) and they give evidence that the ZnGa-related recombination decreases by addition of ammonia. At typical growth conditions the N concentration in the layers was below 1016 cm-3. No influence on the growth rate gas been observed. The ammonia influence is attributed to the competition between As and N species during adsorption on the growing crystal surface.

Minimum of oscillator strength of excitons in ultra-narrow GaAs/AlGaAs quantum wells: theory and experiment

A theoretical and experimental study of the exciton in ultra-narrow quantum wells (QWs) is performed. A crossover from strong (separate localization of electron and hole levels) to weak confinement (with localization of excitonic center of mass) is predicted to occur for decreasing thickness, and is characterized by a minimum of the oscillator strength per unit area. Cathodoluminescence measurements performed on a series of GaAs/Al0.35Ga0.65As QWs with thicknesses from one to eight monolayers show a minimum of the oscillator strength, in agreement with theory, and indicate that the crossover from strong to weak confinement occurs at a thickness of about three monolayers for this composition

Movpe Growth and Properties of Gap Using Nitrogen Bridged Adduct

Amongst the new precursors for the III component in MOVPE there are numerous nitrogen containing compounds. Using those compounds, besides the electrical and optical quality of the grown material, the question of incorporation of nitrogen arises. We present the results of GaP growth with the TMGa-TMN adduct. Photoluminscence at 2 K clearly detects nitrogen as a substitutional dopant. Considering the luminescence features the nitrogen concentration was estimated to be about 10(16)-10(17) cm-3. The residual carrier concentration of the layers is in the range of 10(15) cm-3. No oxygen-related emission was observed. A discussion of the growth and the properties of the material is given.

Ultrathin GaAs layers embedded in AlAs: a perspective for intense short wavelength emission

Abstract Type-II GaAs/AlAs quantum-well samples grown by low-pressure metal-organic vapour-phase epitaxy consisting of 50 periods of either 2 monolayers (ML), 4 ML, 5 ML, 6 ML, or 7 ML GaAs embedded in 28 ML AlAs were under investigation. Even at room temperature dominant type-I luminescence has been observed. The peak wavelength of this emission ranges from 620 to 440 nm and is determined by the GaAs layer thickness. A comparison of the measured transition energies with model calculations applying an effective mass approach and an empirical tight-binding Greens function scheme confirmed this strong dependence. To our knowledge this is the first report on intense yellow, green, and blue luminescence from GaAs.

Ultrathin GaAs layers embedded in AlAs: The observation of intense short-wavelength emission

Type-II GaAs/AlAs multiple-quantum well samples groan by low-pressure metal-organic vapour-phase epitaxy have been investigated. The layered structures consist of 50 periods of either 2 monolayers (ML), 4 ML. 5 ML, 6 ML, or 7 ML GaAs embedded in 28 ML AlAs. Using (100) GaAs substrates 6 degrees misoriented towards the nearest (111)B plane monolayer steps at the AlAs/GaAs/AlAs interfaces with regular terrace widths (2.7 nm) can be seen by high-resolution transmission electron microscopy. In the photoluminescence spectra even at room temperature type-I luminescence is found to be dominant. The peak wavelength of this emission ranges from 620 to 440 nm and is governed by the GaAs layer thickness. The comparison of the measured transition energies with calculations based on an effective mass approach and an empirical tight-binding Greens function scheme shows good agreement. The perfect interface structure of our samples with regular distribution of monolayer steps prevents obviously the loss of photoexcited carriers from the GaAs layers to the surrounding, energetically resonant AlAs material allowing only low type-II luminescence intensity. Furthermore, for our well thicknesses 2D phonons have to be coupled with 3D electrons leading to low electron-phonon interaction.