III-V Detectors

Abstract

The quantum-well infrared photodetector (QWIP) is a relatively new type of semiconductor detector which has a clearly defined spectral response. This study shows that the infrared spectral response of a QWIP can be fine tuned. We have fabricated AlGaAs-GaAs QWIPs, and used proton implantation and rapid thermal annealing to tune the infrared spectral response of these QWIPs by up to 1.4 pm. Multiple proton implants at energies between 200 and 400 keV were used to create homogeneous quantum-well intermixing throughout the de vices' multiple-quantum-well structure. Photoluminescence and photoresponse measurements were used to study the effect of proton implantation on QWIPs for a series of doses up to 3.5 x 1015 protons cm-2. By using a mask during im plantation, a method of constructing a colour sensitive array is proposed. The dynamics in quantum-wells with similar properties to QWIPs were investigated. The capture of electron-hole pairs into a quantum-well increased after the sam ple was intermixed. Thus intermixed QWIPs may exhibit improved electrical response bandwidths. The dynamic properties of a sawtooth superlattice (<5-doped nipt) were ex amined by photoluminescence spectroscopic techniques. The dynamic properties of the sawtooth superlattice were probed using time resolved photoluminescence and carrier lifetime measurements. £-doped sawtooth superlattices are shown to have a tunable bandgap as well as an intensity tunable carrier lifetime. These properties may prove useful in the development of a wavelength tunable inter subband nipi infrared detector. Thermal quenching of photoluminescence from GaAs-InGaAs and AlGaAs-GaAs quantum-wells has been shown to be dependent on the intensity of excita tion. We believe this intensity dependence is related to the presence of saturable non-radiative recombination paths via hetero-interface defects. Additionally, an increase in photoluminescence intensity as a function of temperature has been observed at low temperatures. These results are linked to the presence of sat urable defect states, possibly surface states. Firstly I would like to thank my supervisor, Professor Mike Gal for everything he has taught me during my studies. His enthusiasm, knowledge and advice have helped maintain the direction of this thesis, while the responsibility and freedom he has given me has allowed me to follow some of my own odd ideas. Dr C. Jagadish has been a constant source of encouragement and useful collaboration, both with his group at the Australian National University and with the Chinese Academy of Sciences. Without the expertise, time and facilities of his group this project would not have been possible. Dr. Lap van Dao has constructed the photoluminescence up-conversion sys tem in our laboratory. His skill in lasers and optics is exceptional. Thanks to Lap for many discussions on carrier dynamics in quantum-wells. Sincere thanks to Dr. Nancy Lumpkin for spending so many hours teaching me semiconductor device fabrication and for sharing her excellent methods with me. The fabri...