O.V. Sulima

III-V compound detectors for CO2 DIAL measurements

Profiling of atmospheric carbon dioxide (CO2) is important for understanding the natural carbon cycle on Earth and its influence on global warming and climate change. Differential absorption lidar is a powerful remote sensing technique used for profiling and monitoring atmospheric constituents. Recently there has been an interest to apply this technique, at the 2 μm wavelength, for investigating atmospheric CO2. This drives the need for high quality detectors at this wavelength. Although 2 μm detectors are commercially available, the quest for a better detector is still on. The detector performance, regarding quantum efficiency, gain and associated noise, affects the DIAL signal-to-noise ratio and background signal, thereby influencing the instrument sensitivity and dynamic range. Detectors based on the III-V based compound materials shows a strong potential for such application. In this paper the detector requirements for a long range CO2 DIAL profiles will be discussed. These requirements were compared to newly developed III-V compound infrared detectors. The performance of ternary InGaSb pn junction devices will be presented using different substrates, as well as quaternary InGaAsSb npn structure. The performance study was based on experimental characterization of the devices dark current, spectral response, gain and noise. The final results are compared to the current state-of-the-art InGaAs technology. Npn phototransistor structure showed the best performance, regarding the internal gain and therefore the device signal-to-noise ratio. 2-μm detectivity as high as 3.9x1011 cmHz1/2/W was obtained at a temperature of -20°C and 4 V bias voltage. This corresponds to a responsivity of 2650 A/W with about 60% quantum efficiency.

InGaAsSb/AlGaAsSb Heterojunction Phototransistors for Infrared Applications

High quality infrared (IR) quantum detectors are important for several applications, such as atmospheric remote sensing, chemical detection and absorption spectroscopy. Although several IR detectors are commercially available, with different materials and structures, they provide limited performance regarding the signal-to-noise ratio and the corresponding minimum detectable signal. InGaAsSb/AlGaAsSb heterojunction based phototransistors show strong potential for developing IR sensors with improved performance. In this paper, the performance of a novel n-p-n InGaAsSb/AlGaAsSb heterojunction phototransistor is presented. This performance study is based on experimental characterization of the device dark current, noise and spectral response. Detectivity of 1.7x109 cmHz 1/2/W at 2-μm was obtained at 100°C temperature and 2 V bias voltage. This corresponds to a responsivity of 94.7 A/W and an internal gain of 156 with about 38% quantum efficiency. Reducing the temperature to -30°C allows to increase the bias to 3V and enhance the detectivity to 8.7x1010 cmHz1/2/W at the same wavelength, which corresponds to a responsivity of 386.5 A/W and an internal gain of 288.2 with about 83% quantum efficiency. The device impulse response and linearity, including the corresponding dynamic range, also are presented. Impulse response analysis indicated a settling time of about 1.1 μs at 2V and 100°C, while linearity measurements indicated a constant responsivity in the radiation intensity range of 1.6x10-7 W/cm2 and 31.6 mW/cm2.

Room-temperature AlGaAsSb/InGaAsSb heterojunction phototransistors

We present room-temperature AlGaAsSb/InGaAsSb heterojunction phototransistors (HPT) with a cutoff wavelength (50% of maximum quantum efficiency) of 2.4 μm and 2.15 μm. AlGaAsSb/InGaAsSb HPT structures were grown by molecular beam epitaxy (MBE) or metal-organic chemical vapor deposition (MOCVD). This work is a continuation of a preceding project, which was carried out using liquid phase epitaxy (LPE) grown AlGaAsSb/InGaAsSb/GaSb heterostructures. Although the LPE-related work resulted in the fabrication of an HPT with excellent parameters, MBE and MOCVD - compared to LPE - provides better control over doping levels, composition and width of the AlGaAsSb and InGaAsSb layers, compositional and doping profiles, especially with regard to abrupt heterojunctions. HPT with different diameter of photosensitive area (75, 200, 300 and 1000 μm) were fabricated and characterized. In particular, I-V characteristics, spectral response and noise, as well as detectivity and noise-equivalent-power were determined in a broad range of temperatures and bias voltages. Advantages of HPT integration with diffractive optical elements (DOE) were demonstrated.

Integrated micro-optical multichip module based on an uncooled InGaAsSb∕AlGaAsSb photodetector

This paper focuses on the integration of InGaAsSb photodetectors along with micro-optics in order to realize a prototype system that can achieve a stronger response during atmospheric profiling and spectroscopy measurements. The integration of the detector was executed using a novel conductive-adhesive-based flip-chip integration process. The design, fabrication, and integration of the constituent technologies and experimental results from their characterization are presented.