Showing papers by "Thomas F. Kuech published in 1986"

Determination of the interdiffusion of Al and Ga in undoped (Al,Ga)As/GaAs quantum wells

Abstract: We have employed photoluminescence spectroscopy to determine the temperature dependence of the interdiffusion coefficient of Al and Ga in GaAs/Al03Ga07As quantum wells The position of the photoluminescence peaks, due to the n=1 electron to heavy‐hole transition, was measured before and after annealing the samples A variational calculation was employed to determine the expected position of these photoluminescence peaks and from this a value of the interdiffusion coefficient was extracted The interdiffusion process is characterized by an activation energy of about 6 eV leading to an interdiffusion coefficient at 850 °C of 4×10−19 cm2/s This technique allows for the measurement of small diffusion coefficients in a wide variety of material systems

Pressure dependence of GaAs/AlxGa1−xAs quantum‐well bound states: The determination of valence‐band offsets

Abstract: We report experiment and theory on the pressure dependence of quantum‐well bound states formed in the GaAs/AlxGa1−xAs heterostructure system. Using MQW’s and SL’s of various barrier compositions x, we trace in photoluminescence (8 K), and in full‐scale pseudopotential calculation, the pressure‐induced evolution of the lowest spatially confined states within the wells. With increasing pressure Γ‐confined states follow the shift to higher energies of the direct GaAs band gap. At critical pressures a crossing occurs between these Γ bound states and the barrier indirect X states. Here, Γ intensities plunge and new emission tracking the X edges appears. Confirmed in wave function calculation, these new transitions occur across the heterointerface, between X‐confined electrons within the AlxGa1−xAs and Γ‐confined holes within the GaAs. Arising from valence‐offset‐induced staggered band alignment, critical pressures for observation of these states decrease with increasing Al mole fraction. We thus obtain, with p...

Interdiffusion of Al and Ga in (Al,Ga)As/GaAs Quantum Wells

Abstract: We have employed photoluminescence spectroscopy to determine the interdiffusion of Al and Ga in (Al,Ga)As/GaAs quantum wells. The luminescence due to the n=l electron to heavy hole transition in these wells before and after anneal was measured. A variational calculation was employed to determine the expected position of this luminescence peak both before and after the anneal. A single diffusion coefficient, D , was used to model the interdiffusion of the Al and Ga and from the shifted position of the luminescence peaks under various anneal conditions of time and temperature its value was determined. These measurements were performed as a function of temperature to yield ΔE where D = D 0 e -ΔE/KT. This diffusion coefficient was also studied as a function of the initial Al composition in the cladding layers which ranged from 0.3 to 1.0.

Picosecond photoresponsive element

Abstract: Picosecond response photoconductors and photoresponsive elements can be provided that retain high carrier mobility and yet have short lifetime by providing on a crystal mismatched substrate (1) a textured layer (2) of domain regions (3) wherein the domain size is such that the lifetime (t) is proportional to the square of the size (S²) divided by the diffusion coefficient (D) of the semiconductor (i.e. t ≈ S²/D) material. The crystalline orientation in the domains with respect to the substrate is maintained. An embodiment is an approximately 0.1 micron thick textured layer of GaAs (2) grown on a hexagonal monocrystalline Al₂O₃ substrate (1) having domains approximately 1.0 micron with a carrier lifetime about 5 picoseconds and a carrier mobility of about 80 cm² volt⁻¹ sec⁻¹.