Far Infrared Studies of III-V and II-VI 2 and 3 Dimensional Semiconductors
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This thesis reports the behaviour of impurities in IIIV semiconductors using the sensitive technique of far infrared photoconduction (FIRPC) at low temperatures and at magnetic fields up to 10T. The thesis reports the effects of inadvertent and intentional impurities in both bulk epitaxial and low dimensional structure systems grown by molecular beam epitaxy (MBE).

High mobility bulk n-GaAs has been investigated and the present measurements shows a variety of optical transitions involving the shallow donor impurities. The first observation of the D transitions in MBE n-GaAs is reported as well as central-cell splitting of the impurity shifted cyclotron resonance (ISCR). Inadvertent contaminants are identified by measurements of central-cell splittings and a clear observation of the "bottle-neck" effect is reported. A distinct splitting of the cyclotron resonance is seen and is taken as evidence of transitions between spin-split higher Landau levels.

Measurements on high mobility GaAs/AlGaAs heterojunctions have shown a cyclotron resonance splitting observed only in photoconduction. This has been explained using a coupled oscillator model of impurities that have migrated to the interface during growth.

GaAs/AlGaAs multi-quantum wells (MQW) have been grown with intentional silicon doping in the well centres. Zeeman spectroscopy of the 1s0->2p+1 transition has been performed up to 10 T and show linewidths much narrower than for other reported samples. Transitions involving higher states of the confined impurity are clearly seen in these samples.

Time-resolved far infrared photoconduction measurements have been carried out on bulk n-InP, GaAs/AlGaAs heterojunctions, and multi-quantum wells. These measurements have enabled the investigation of electron recombination dynamics after the termination of the laser pulse. The time response of suitably doped MQW samples indicates potential as fast, sensitive, detectors of long wavelength (100 um) radiation.

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(c) 2006 Richard Grimes