Optoelectronic devices operating in the mid-wave (3-5 Μm) and long-wave (8-12 Μm) infrared (IR) regions of the electromagnetic spectrum are of a great interest for academic and industrial applications. Due to the lack of atmospheric absorption, devices operating within these spectral bands are particularly useful for spectroscopy, imaging, and dynamic scene projection. Advanced IR imaging systems have created an intense need for laboratory-based infrared scene projector (IRSP) systems which can be used for accurate simulation of real-world phenomena occurring in the IR. These IRSP systems allow for reliable, reproducible, safe, and cost-effective calibration of IR detector arrays. The current state-of-the-art technology utilized for the emitter source of IRSP systems is thermal pixel arrays (TPAs) which are based on thin film resistor technology. Thermal pixel array technology has fundamental limitations related to response time and maximum simulated apparent temperature, making them unsuitable for emulation of very hot (> 700 K) and rapidly evolving scenes. Additionally, there exists a need for dual wavelength emitter arrays for IRSP systems dedicated to calibration of dual wavelength detector arrays. This need is currently met by combining the spectral output from two separate IRSP systems. This configuration requires precise alignment of the output from both systems and results in the maximum radiance being limited to approximately half that of the capability of a given emitter array due to the optics used to combine the outputs. The high switching speed inherent to IR light-emitting diodes (LEDs) and the potential for high power output makes them an appealing candidate to replace the thermal pixel arrays used for IRSP systems. To this end, research has been carried out to develop and improve the device performance of IR LEDs based on InAs/GaSb type-II superlattices (T2SLs). A common method employed to achieve high brightness from LEDs is to incorporate multiple active regions, coupled by tunnel junctions. Tunnel junctions must provide adequate barriers to prevent carrier leakage, while at the same time remain low in tunneling resistance to prevent unwanted heating. The performance of two tunnel junction designs are compared in otherwise identical four stage InAs/GaSb superlattice LED (SLED) devices for application in IRSP systems. This research culminated in the development of a 48 Μm pitch, 512$times512 individually addressable mid-wave IR LED array based on a sixteen stage, InAs/GaSb T2SL device design. This array was hybridized to a read-in integrated circuit and exhibited a pixel yield greater than 95 %. Projections based on single element emitter results predict this array will be able to achieve a peak apparent temperature of 1350 K within the entire 3-5 Μm band. These results demonstrate the feasibility of emitter arrays intended for IRSP systems based on InAs/GaSb SLED devices. Additionally, a dual wavelength 48 Μm pitch, 8x8 emitter array based on InAs/GaSb T2SL LEDs was developed and demonstrated. This design incorporates two separate, 16 stage InAs/GaSb SL active regions with varying InAs layer thicknesses built into a single vertical heterostructure. The device architecture is a three terminal device allowing for independent control of the intensity of each emission region. Each emitter region creates a contiguous pixel, capable of being planarized and mated to drive electronics.

abstract: Sb-based type-II superlattices (T2SLs) are potential alternative to HgCdTe for infrared detection due to their low manufacturing cost, good uniformity, high structural stability, and suppressed Auger recombination. The emerging InAs/InAsSb T2SLs have minority carrier lifetimes 1-2 orders of magnitude longer than those of the well-studied InAs/InGaSb T2SLs, and therefore have the potential to achieve photodetectors with higher performance. This work develops a novel method to measure the minority carrier lifetimes in infrared materials, and reports a comprehensive characterization of minority carrier lifetime and transport in InAs/InAsSb T2SLs at temperatures below 77 K. A real-time baseline correction (RBC) method for minority carrier lifetime measurement is developed by upgrading a conventional boxcar-based time-resolved photoluminescence (TRPL) experimental system that suffers from low signal-to-noise ratio due to strong low frequency noise. The key is to modify the impulse response of the conventional TRPL system, and therefore the system becomes less sensitive to the dominant noise. Using this RBC method, the signal-to-noise ratio is improved by 2 orders of magnitude. A record long minority carrier lifetime of 12.8 μs is observed in a high-quality mid-wavelength infrared InAs/InAsSb T2SLs at 15 K. It is further discovered that this long lifetime is partially due to strong carrier localization, which is revealed by temperature-dependent photoluminescence (PL) and TRPL measurements for InAs/InAsSb T2SLs with different period thicknesses. Moreover, the PL and TRPL results suggest that the atomic layer thickness variation is the main origin of carrier localization, which is further confirmed by a calculation using transfer matrix method. To study the impact of the carrier localization on the device performance of InAs/InAsSb photodetectors, minority hole diffusion lengths are determined by the simulation of external quantum efficiency (EQE). A comparative study shows that carrier localization has negligible effect on the minority hole diffusion length in InAs/InAsSb T2SLs, and the long minority carrier lifetimes enhanced by carrier localization is not beneficial for photodetector operation. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2016

abstract: The first part of this dissertation reports the study of the vertical carrier transport and device application in InAs/InAs1-xSbx strain-balanced type-II superlattice. It is known that the low hole mobility in the InAs/InAs1-xSbx superlattice is considered as the main reason for the low internal quantum efficiency of its mid-wave and long-wave infrared photodetectors, compared with that of its HgCdTe counterparts. Optical measurements using time-resolved photoluminescence and steady-state photoluminescence spectroscopy are implemented to extract the diffusion coefficients and mobilities of holes in the superlattices at various temperatures from 12 K to 210 K. The sample structure consists of a mid-wave infrared superlattice absorber region grown atop a long-wave infrared superlattice probe region. An ambipolar diffusion model is adopted to extract the hole mobility. The results show that the hole mobility first increases from 0.2 cm2/Vs at 12 K and then levels off at ~50 cm2/Vs as the temperature exceeds ~60 K. An InAs/InAs1-xSbx type-II superlattice nBn long-wavelength barrier infrared photodetector has also been demonstrated with a measured dark current density of 9.5×10-4 A/cm2 and a maximum resistance-area product of 563 Ω-cm2 at 77 K under a bias of -0.5 V. The Arrhenius plot of the dark current density reveals a possible high-operating-temperature of 110 K.The second part of the dissertation reports a lift-off technology using a water-soluble sacrificial MgTe layer grown on InSb. This technique enables the seamless integration of materials with lattice constants near 6.5 Å, such as InSb, CdTe, PbTe, HgTe and Sn. Coherently strained MgTe with a lattice constant close to 6.5 Å acts as a sacrificial layer which reacts with water and releases the film above it. Freestanding CdTe/MgxCd1-xTe double-heterostructures resulting from the lift-off process show increased photoluminescence intensity due to enhanced extraction efficiency and photon-recycling effect. The lifted-off thin films show smooth and flat surfaces with 6.7 Å root-mean-square roughness revealed by atomic-force microscopy profiles. The increased photoluminescence intensity also confirms that the CdTe/MgxCd1-xTe double-heterostructures maintain the high optical quality after epitaxial lift-off. / Dissertation/Thesis / Doctoral Dissertation Electrical Engineering 2020