<title>Use of ion implantation for the creation of ultrafast photodetector materials and tuning of quantum well infrared photodetectors</title>

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There has been a great revival of interest in the area of ultrafast photodetectors after the discovery of low temperature (LT) MBE-grown GaAs [1-3]. These detectors have found numerous applications in picosecond electrical pulse generation and sampling, and as main components of spectroscopic arrangements for terahertz frequency range. The unique properties of LT GaAs such as short carrier lifetimes and high resistivity made it a promising material for ultrafast photoconductive switches and photodetectors. It has been reported that ion implanted material may provide an alternative material for these applications [4-6]. Defects introduced by implantation may act as traps or recombination centres that have large carrier capture cross sections which shorten the carrier lifetimes significantly. The work presented below is an overview of how ion implantation could be used to modify the properties of GaAs and InP for ultrafast photodetector applications. Also, in the area of quantum well infrared photodetectors (QWIPs), there has been much effort in developing the technology for multi-color QWIPs [7,8]. These devices are highly desirable in advanced high performance infrared (IR) systems as it provides not only the spatial information of the image but also the spectral information. Although the functionality of these devices could be designed right from the epitaxy stage, it requires complicated structures and processing steps. In this paper we will demonstrated an alternative method of realizing the multi-color QWIP by a technique known as intermixing. By implantation, the band structure of the quantum wells (QWs) could be modified and hence tune the detection wavelength of the device.