Defect engineering of InP and InGaAs for optoelectronic applications

Abstract

InP and InGaAs lattice matched to InP hold a special place in the optoelectronics industry because of their room temperature bandgaps of 1.27 and 0.73 e V; these translate into emission/ detection wavelengths of - 0.9 and 1.6 μm As such, they are ideal for the development of long wavelength technology, in particular the 1.3 and 1.5 5 μm emissions that are achievable in lattice matched InGaAs/InP systems, which can be transmitted through optical fibre with low signal loss for long distance telecommunications. However, the device processing technologies of InP and InGaAs are less mature than those of, say, GaAs or Si, and continuing research is needed to take full advantage of the intrinsic properties of these materials. One branch of current research involves defect production and diffusion, which is known to greatly modify the electrical and optical properties of these semiconductors. Ion implantation is one way of introducing a large amount of defects, and a significant part of this work focuses on understanding the changes to the electrical and optical properties of InP and InGaAs resulting from such implantation. Combined with structural studies, an insight into multiple defective layers of varying optical and electrical properties after implantation has been gleaned. In both InP and InGaAs, implantation was found to result in large concentrations of shallow donors which reduced the resistance of the semiconductor. Depending on the element implanted, this reduced resistivity was concentrated in one or two layers within the damaged region. Implantation also resulted in the creation of non-radiative recombination centers, which in some cases reduced the carrier lifetime of the material to the sub-picosecond range. With the aim of creating materials suitable for ultrafast photodetectors, this work has successfully found ways to increase the resistivity of both implanted InP and InGaAs while keeping the response times as low as possible. In addition to the creation of defect.s, their diffusion was induced using annealing techniques, and the corresponding structural, electrical and optical changes observed. 1bis provided another parameter for varying the properties of defective InP and InGaAs with device applications in mind. Annealing, in combination v.1:ith ion implantation and dielectric capping layer techniques, was also used to promote interdiffusion of InP /InGaAs and InGaAs/ AlGainAs quantum well structures, thereby tuning the emission/ detection -wavelengths. The damage accumulation processes resulting from implantation in InP and InGaAs at different temperatures was found to strongly influence the degree of interdiffusion achieved. 1bis was related to whether implantation conditions were conducive to fonnation of point defects or more complex clusters and loops, since the fonner were more mobile and thus good vectors for interdiffusion. Strain, as well as the inteiplay of group III and group V interdiffusion and surface chemistry, was found to play a major role in the amount of wavelength tuning that was achievable. The quantum well structures studied showed a great deal of versatility in temis of the obtained peak emission wavelength shifts, and in some cases this emission/ detection wavelength was actually shifted to larger values (redshifted), something not achievable in standard interdiffusion of AlGaAs/ GaAs and InGaAs/ Ga.As quantum wells. 1bis wotk has provided clear advances in the understanding of defective InP and InGaAs with direct applications to devices. By varying implant dose, initial free carrier concentration, annealing temperature and dielectric deposition parameters, bulk materials and heterostructures can be obtained with the ideal characteristics for optoeletronic applications.