Publications by Andrew Turberfield


OPTICAL MEASUREMENTS OF CORRELATED STATES OF 2-DIMENSIONAL ELECTRONS IN GAAS AT LOW-TEMPERATURES AND HIGH MAGNETIC-FIELDS

PHYS SCRIPTA T39 (1991) 223-229

JF RYAN, RG CLARK, RA FORD, CT FOXON, JJ HARRIS, SR HAYNES, AJ TURBERFIELD, PA WRIGHT


OPTICAL-DETECTION OF THE INTEGER AND FRACTIONAL QUANTUM HALL-EFFECTS IN GAAS AT MILLIKELVIN TEMPERATURES

253 (1991) 27-34

AJ TURBERFIELD, SR HAYNES, PA WRIGHT, RA FORD, RG CLARK, JF RYAN, JJ HARRIS, CT FOXON


OPTICAL STUDIES OF TUNNELING IN DOUBLE BARRIER DIODES

SUPERLATTICES AND MICROSTRUCTURES 9 (1991) 357-361

SR ANDREWS, AJ TURBERFIELD, BA MILLER


OPTICAL SPECTROSCOPY OF GAAS IN THE EXTREME QUANTUM LIMIT - INTEGER AND FRACTIONAL QUANTUM HALL-EFFECT, AND ONSET OF THE ELECTRON SOLID

PHYSICA B 169 (1991) 336-354

RG CLARK, RA FORD, SR HAYNES, JF RYAN, AJ TURBERFIELD, PA WRIGHT, FIB WILLIAMS, G DEVILLE, DC GLATTLI, JR MALLETT, M VANDERBURGT, PMW OSWALD, F HERLACH, CT FOXON, JJ HARRIS


OPTICAL-DETECTION OF THE INTEGER AND FRACTIONAL QUANTUM HALL-EFFECTS IN GAAS

(1990) 805-808

AJ TURBERFIELD, SR HAYNES, PA WRIGHT, RA FORD, RG CLARK, JF RYAN, JJ HARRIS, CT FOXON


Optical detection of the integer and fractional quantum Hall effects in GaAs.

Phys Rev Lett 65 (1990) 637-640

AJ Turberfield, SR Haynes, PA Wright, RA Ford, RG Clark, JF Ryan, JJ Harris, CT Foxon


INVESTIGATION OF INTER-VALLEY SCATTERING AND HOT PHONON DYNAMICS IN GAAS QUANTUM WELLS USING FEMTOSECOND LUMINESCENCE INTENSITY CORRELATION

SUPERLATTICES AND MICROSTRUCTURES 6 (1989) 199-202

AM DEPAULA, RA TAYLOR, CWW BRADLEY, AJ TURBERFIELD, JF RYAN


Investigation of inter-valley scattering and hot phonon dynamics in GaAs quantum wells using femtosecond luminescence intensity correlation

Superlattices and Microstructures 6 (1989) 199-202

AM de Paula, RA Taylor, CWW Bradley, AJ Turberfield, JF Ryan

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.


MAGNETIC FIELD-DEPENDENT HOT CARRIER RELAXATION IN GAAS QUANTUM WELLS

SOLID-STATE ELECTRONICS 31 (1988) 387-390

AJ TURBERFIELD


Photoluminescence study of two-dimensional carriers in the presence of in-plane magnetic fields

Surface Science 170 (1986) 624-628

AJ Turberfield, JF Ryan, JM Worlock

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.


Time-resolved photoluminescence from hot two-dimensional carriers in GaAsGaAlAs MQWS

Surface Science 170 (1986) 511-519

JF Ryan, RA Taylor, AJ Turberfield, JM Worlock

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.


TIME-RESOLVED PHOTOLUMINESCENCE FROM HOT TWO-DIMENSIONAL CARRIERS IN GAAS-GAALAS MQWS

SURFACE SCIENCE 170 (1986) 511-519

JF RYAN, RA TAYLOR, AJ TURBERFIELD, JM WORLOCK


PICOSECOND PHOTOLUMINESCENCE MEASUREMENTS OF LANDAU-LEVEL LIFETIMES AND TIME-DEPENDENT LANDAU-LEVEL LINBROADENING IN MODULATION-DOPED GAAS-GAALAS MULTIPLE QUANTUM WELLS

PHYSICA B & C 134 (1985) 318-322

JF RYAN, RA TAYLOR, AJ TURBERFIELD, JM WORLOCK


HOT ELECTRON RELAXATION AND TRAPPING IN MODULATION-DOPED GaAs/GaA1As MULTIPLE QUANTUM WELL HETEROSTRUCTURES.

(1985) 567-570

JF Ryan, RA Taylor, AJ Turberfield, A Maciel, JM Worlock, AC Gossard, W Wiegmann

There is much current interest in determining the energy relaxation processes of hot carriers confined in quantum well heterostructures. We present measurements of time-resolved photoluminescence from hot carriers and from carrier recombination at shallow traps. The experimental technique is basically the same as described previously except that the laser (h upsilon //L equals 1. 76 eV) excites carriers only in the GaAs layers.


Picosecond photoluminescence measurements of Landau level lifetimes and time dependent Landau level linebroadening in modulation-doped GaAs-GaAlAs multiple quantum wells

Physica B+C 134 (1985) 318-322

JF Ryan, RA Taylor, AJ Turberfield, JM Worlock

We report the first picosecond time-resolved photoluminescence measurementsof hot-carrier relaxation in a modulation-doped GaAs-GaAlAs MQW in the presence of strong magnetic fields. We have measured the lifetimes of carriers in excited Landau levels and have determined the time-dependent carrier temperature. We find that the cooling rate is slower in applied field tthan at B=0; also there is a significant increase in the cooling rate for B {greater-than or approximate} 10T. We report also the observation of highly time-dependent linewidths of the Landau levels. © 1985.


MEASUREMENTS OF HOT CARRIER RELAXATION AND RECOMBINATION IN GaAs QUANTUM WELLS BY PICOSECOND OPTICAL PROBING.

IEE Colloquium (Digest) (1984)

JF Ryan, RA Taylor, AJ Turberfield

In this paper the authors show how picosecond time-resolved photoluminescence can be used to probe the energy relaxation of hot carriers in semiconductor structures. In addition, by measuring the variation of luminescence lifetime with carrier density one can obtain information about radiative and nonradiative decay processes. These processes are important in all photonic devices, but especially so in structures where interfaces may have a particularly strong influence.


TIME-RESOLVED PHOTOLUMINESCENCE OF TWO-DIMENSIONAL HOT CARRIERS IN GAAS-ALGAAS HETEROSTRUCTURES

PHYSICAL REVIEW LETTERS 53 (1984) 1841-1844

JF RYAN, RA TAYLOR, AJ TURBERFIELD, A MACIEL, JM WORLOCK, AC GOSSARD, W WIEGMANN


Time-resolved photoluminescence of two-dimensional hot carriers in GaAs-AlGaAs heterostructures

Physical Review Letters 53 (1984) 1841-1844

JF Ryan, RA Taylor, AJ Turberfield, A Maciel, JM Worlock, AC Gossard, W Wiegmann

We have studied the picosecond time dependence of luminescence from a two-dimensional electron system following absorption of an ultrashort light pulse. From our measurements we determine the temporal evolution of the carrier temperature, finding that the cooling of hot carriers is suppressed by a factor 60 below that predicted on a three-dimensional nondegenerate-electron model. Additionally, we determine the electron-hole radiative life-time and invoke a hole trap to explain shortened luminescence lifetimes at low carrier densities. © 1984 The American Physical Society.

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