Multi-spectral Photodetectors on Gallium Arsenide Substrates using Metamorphic Epitaxy and Hybrid III-V Heterostructures

Epitaxially-integrated, vertically-aligned, multi-band photodetector architecture has been demonstrated in this dissertation, via the successful growth and fabrication of metamorphic back-to-back n-i-p/p-i-n InzGa 1-zP/InxGa1-xAs visible/near-IR dual-detector devices on GaAs substrates. InzGa1-zP and InxGa 1-xAs alloys with lattice constants between GaAs and InP were chosen for this work due to the richness of direct bandgaps (corresponding to visible and near-IR detector cut-off wavelengths) available. Bandgap tunability for the detector materials was achieved using lattice grading by utilizing metamorphic InxGa1-xAs step-graded buffers grown using solid-source molecular beam epitaxy. In addition to its importance in multi-spectral detection, bandgap tunability also facilitates the maximization of detector performance at target wavelengths, which was demonstrated by the high-performance In zGa1-zP and InxGa1-xAs p-i-n photodetectors achieved with different cut-off wavelengths.;For buffer design optimization, a comprehensive study of the impact of InxGa1-xAs metamorphic buffer steps design on metamorphic material quality, including TDD and phase segregation, and its corresponding impact on photodetector performances were performed. It was found that the variation in TDD (calculated using plan-view TEM and electron-beam induced current (EBIC) experiments), within the range of values investigated in this work (low-105 to low-107 cm-2), has only a minimal impact on the InxGa1-xAs p-i-n photodetector properties such as dark current. This is attributed to the high intrinsic carrier concentration value of the low bandgap InxGa1-xAs resulting in higher diffusion current, effectively masking the effect of SRH generation-recombination effects. In addition, it was observed that the effect of residual strain in the final buffer layer has no measurable impact on In xGa1-xAs p-i-n photodetectors for InxGa1-x As with In0.68Ga0.32P p-i-n photodetectors were found to be extremely sensitive to the presence of residual or interface strain resulting in phase segregation of InGaP into In-rich and Ga-rich areas, which in turn resulting in a significant increase in the TDD values. As a result of the increased TDD and phase segregation, In0.68Ga0.32P p-i-n photodetectors with even slight tensile interface strain, displayed orders of magnitude higher dark current densities compared to devices with no strain. To address this, all the different photodetectors utilized a compositional overshoot layer as the final buffer step followed by a perfectly lattice-matched step-back layer to eliminate any residual strain in the photodetector layers.;In terms of the dual-detector performance, the required simultaneous and independent operation of sub-detectors was achieved using a back-to-back n-i-p/p-i-n design combined with optimized photomask design and fabrication processes. This allowed the realization of desired results such as passage of light through the top sub-detector before being absorbed by the bottom sub-detector. The prototype In0.61Ga0.39P/ In0.14 Ga0.86As demonstrated excellent material and photodetector properties including complete electrical isolation of the sub-detector elements (no measureable electrical cross-talk or charge leakage) and relatively low optical cross-talk of In0.61Ga0.39P sub-detector device layers. The sub-detectors closely matched the individual photodetector properties of low, room temperature reverse bias (-2 V) dark current densities, high responsivities and high specific detectivity values of 4x10-8 A·cm-2, 0.41 A/W and 8.6x1011 cm·Hz1/2/W for the In0.14Ga 0.86As sub-detectors (at 980 nm) and 7x10-12 A·cm -2, 0.30 A/W and 2.0x1014 cm·Hz 1/2/W for the In0.61Ga0.39P sub-detectors (at 680 nm), respectively, confirming the high-level of success achieved with the integration process. (Abstract shortened by UMI.)...