Highly-Strained Mid-Infrared Diode Lasers (Topic 4.2 - Optoelectronics)
Abstract
The objective of the proposed research is to develop higher efficiency mid-IR laser diodes by pursuing novel molecular beam epitaxy growth regimes. Two thrusts will be pursued involving Sb-based semiconductors: 1) the use of bismuth as a surfactant to improve the critcial thickness for longer wavelengths to obviate the need for metamorphic buffer layers proven unreliable for reliable laser operation, and 2) growth of new dilute-bismide semiconductors with similar goals. More specific goals and approaches to the proposed research are given below. In the first 12 months, the primary target will be to increase the emission wavelength using further reduced growth temperature and strain-compensated (In)GaAlAsSb barriers. Increased hole confinement will be pursued via appropriate heterostructure crystal growth to mitigate hole leakage and study its effects on laser performance, particularly the characteristic temperatures for threshold current (TO) and external efficiency (Tl). In the optional second 12 month period, the materials investigation will continue by introducing bismuth as a surfactant and/or lattice-constituent to increase the critical thickness, focusing on increasing the number ofQWs that can be grown at longer wavelengths to mitigate gain saturation. The anticipated result is that this will bring significant reduction to laser threshold current density and characteristic temperatures. In the optional third 12 month period, the study as to whether bismuth as a surfactant and/or lattice-constituent (in concert with reduced substrate temperature) will continue to be pursued to see if one of them will enable an increased level of strain that can be introduced into the QW active region without degradation. They will also fabricate prototype lasers using the most successful growth regimes. The anticipated goal is significantly improved laser performance with increasing strain, due to reduced Auger recombination and superior hole confinement. If successful, this will afford a new paradigm to further extend the reach of diode lasers into the mid-IR. To pursue the goals above, certain methods and measurment techniques will be pursued. For starters, mapping out the critical thickness, as a function of the growth parameter space, may seem prohibitive in terms of the number of samples required because there are many important variables that must be considered (bismuth flux, QW strain, composition, growth temperature, V/llI flux ratios, As/Sb flux ratio, growth rate, etc.). However, the PI has a multi-beam optical stress sensor (MOS) installed on his As/Sb MBE system, which can measure strain state in real-time in situ. As illustrated in Figure lOa, this will allow them to determine the critical thickness (i.e. the maximum number ofunrelaxed QWs) that can be grown under a given set of growth conditions in a single growth run, rather than growing many samples and performing reciprocal space mapping on each. This capability will make the proposed studies feasible with the proposed budget. The instrumentation and its sensitivity are discussed in the proposal (Section H). The use of the MOS (proposed) to map out the general growth parameter space, complemented by growths of promising active regions in an appropriate test structure (i.e. with wide bandgap AlAsSb carrier blocking layers) for full characterization with PL, excitation dependent PL, and HR-XRD (both (omega)-2(theta) and reciprocal space mapping) to determine their suitability as laser active regions, followed by laser demonstration. As appropriate, they will send active regions to collaborators at Wroclaw University in Poland for band-offset measurements using photo-/electroreflectance (PR/ER) and to our collaborators at CU-Boulder for Auger recombination measurements.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jan 12, 2017
- Source ID
- W911NF1510612
Entities
People
- Seth R. Bank
Organizations
- Army Contracting Command
- United States Army
- University of Texas at Austin