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.

Abstract:

Picosecond time-resolved measurements of luminescence from hot carriers confined in GaAsGaAlAs multiple quantum wells show that energy loss rates are substantially slower than those predicted for 2D carriers. We review our recent experiments and present results for photoexcitation of (1) GaAs layers only, (2) both GaAs and GaAlAs layers. We compare the energy loss rates in samples with different well widths. Finally, we present measurements of hot 2D carrier relaxation in the presence of high magnetic fields; at low fields the energy loss rate is reduced, but for B > 9 T we observe a rapid increase. © 1986.