title: Structural, compositional and ICP processing analysis of CBE grown InGaAsN/GaAs
Creators: name: Charles Stewart. Thomas, Simon
Publisher: name: University of Liverpool Repository
Year: 2023

description: This thesis details the structural and elemental analysis of the III-V quaternary InGaAsN, and subsequent post growth plasma processing of the alloy. The aim of the work was to investigate the varying properties of the material with respect to the CBE growth conditions during deposition. Primarily this was with the objective of producing 1.3J.I.IIl emitting material for quantum well laser diodes. However the large scope of this complex alloy in terms of band structure and lattice variability will make it suitable for a range of applications provided high structural quality can be maintained. Photoluminescent emission with near 1.3J.1m wavelength has been demonstrated for both lattice-matched and compressively strained variants of InGaAsN/GaAs in quantum well form. Homogeneous QW material has been produced for various element fractions with high structural quality through close monitoring of the N and In concentrations. However a three-dimensional growth pattern becomes dominant when increased band gap tailoring is attempted, this is particularly evident when raised nitrogen levels are employed. The miscibility gap introduced by this element disrupts growth surface bonding conditions resulting in a preferential phase segregated defective material. Surface nitridation prior to InGaAsN growth can induce quantum dot or island formation directly on the GaAs buffer surface. Near 1.3J.1mwavelength emission has also been achieved from a quantum dot form of the alloy. A high level of sensitivity in the structural quality of the material with respect to substrate temperature during growth was also demonstrated, lower temperature giving the best results. Poor optical properties can be improved with the application of a post growth high temperature anneal process .Thin film InGaAsN/GaAs has only been produced homogeneously up to a layer thickness of -50nm, and this was achieved using a compressively strained form of the alloy. Lattice-matched material grows in a very disordered and defective manner, this is thought to be due to the raised N fraction required. Higher N containing InGaAsN/GaAs compounds, and surface pre-nitridation, lead to the development of completely phase-segregated epilayer. A cellular-like microstructure becomes dominant consisting of InGaAs volumes encompassed by a highly N-rich Ga(As)N interlayer. Three-dimensional growth is thought to originate from the preferential grouping of the component elements on the various facets of the growth surface, which can be affected by In and N concentrations and growth temperature. Production of high structural and optical quality InGaAsN/GaAs requires the use of non-optimal growth conditions, which may prove problematic particularly in CBE. Material quality still requires refinement, however InGaAsN/GaAs alloys look very promising for a range of optoelectronic devices. ICP processing of thin film InGaAsN/GaAs has shown to be very sensitive to the alloy microstructure for both SiC4 and Cl-.Ar etch chemistries. However highly anisotropic etches at high etch rates with minimal surface damage have been demonstrated. The higher power ion-assisted set-up has proven more effective than the more chemically assisted material removal in all cases. Alloys with both increased N or In give higher etch rates, and in non-optimised conditions In redeposition may become problematic for the chemistries investigated. ICP etching has indicated itself to be a very promising process for III-V device production, but in the case ofInGaAsN/GaAs quality will be dependent on the compound itself. Thin film InGaAsN/GaAs has only been produced homogeneously up to a layer thickness of -50nm, and this was achieved using a compressively strained form of the alloy. Lattice-matched material grows in a very disordered and defective manner, this is thought to be due to the raised N fraction required. Higher N containing InGaAsN/GaAs compounds, and surface pre-nitridation, lead to the development of completely phase-segregated epilayer. A cellular-like microstructure becomes dominant consisting of InGaAs volumes encompassed by a highly N-rich Ga(As)N interlayer. Three-dimensional growth is thought to originate from the preferential grouping of the component elements on the various facets of the growth surface, which can be affected by In and N concentrations and growth temperature. Production of high structural and optical quality InGaAsN/GaAs requires the use of non-optimal growth conditions, which may prove problematic particularly in CBE. Material quality still requires refinement, however InGaAsN/GaAs alloys look very promising for a range of optoelectronic devices. ICP processing of thin film InGaAsN/GaAs has shown to be very sensitive to the alloy microstructure for both SiC4 and Cl-.Ar etch chemistries. However highly anisotropic etches at high etch rates with minimal surface damage have been demonstrated. The higher power ion-assisted set-up has proven more effective than the more chemically assisted material removal in all cases. Alloys with both increased N or In give higher etch rates, and in non-optimised conditions In redeposition may become problematic for the chemistries investigated. ICP etching has indicated itself to be a very promising process for III-V device production, but in the case ofInGaAsN/GaAs quality will be dependent on the compound itself. This thesis describes an account of the research that was undertaken with the supervision of Dr. P. Chalker and Dr. T. J. Bullough in the Department Engineering, The University of Liverpool between the period of October 1999 and September 2003. All of the research is original and has not been submitted for degree from this or any other university. Where applicable the work and results of other people have been included and due acknowledgement has been made. A complete and extensive list of references is presented at the end of this thesis.