Professor Andrew Turberfield

Abstract:

Photoluminescence intensity correlation measurements of GaAs quantum wells using 120 fs laser pulses show relatively slow relaxation times ≤ 10 ps at high energy close to the L valley conduction band minimum. This value is consistent with recent measurements of the L → Γ scattering time. However, theoretical estimates show that nonequilibrium phonon effects can also give rise to slow relaxation on this timescale.

Abstract:

We have measured the effect of in-plane magnetic fields on the photoluminescence of 2D carriers confined in a modulation-doped GaAsAlGaAs MQW heterostructure. The most dramatic effect is a large increase, and eventual saturation at high fields, of the intensity of radiative recombination at interface acceptors (binding energy ∼ 10 meV). We explain this as a result of field-induced spreading of the confined wave functions toward the barriers. We show this behavior to be qualitatively consistent with an analytically soluble model which combines the in-plane magnetic field with harmonic quantum well confinement to give a 1D composite oscillator. The low field spreading is due to linear displacement of the oscillator centers with B; at higher fields the magnetic field confinement shrinks the wave functions, and they recede from the interfaces. We observe also a diamagnetic shift and a spectral narrowing of the band-to-band recombination. These effects are confirmed quantitatively with the composite oscillator model. © 1986.