Title of Presentation: Phototransistors Development and Their Applications to Lidar
Primary (Corresponding) Author: M.Nurul Abedin
Organization of Primary Author: NASA Langley Research Center
Co-Authors: T.F. Refaat, S. Ismail, and U.N. Singh
Abstract: Custom-designed two-micron phototransistors have been developed using Liquid Phase Epitaxy (LPE), Molecular Beam Epitaxy (MBE) and Metal-Organic Chemical Vapor Deposition (MOCVD) techniques under Laser Risk Reduction Program (LRRP) and characterized them at Langley's Detector Characterization Laboratory. It appears that the LPE-grown phototransistor’s performances, such as responsivity, noise-equivalent-power, and gain, are better than MBE- and MOCVD-grown phototransistors. Lidar tests have been conducted under 2-μm CO2 Differential Absorption Lidar (DIAL) Instrument Incubator Program (IIP) using LPE- and MBE-grown phototransistors, and commercial InGaAs avalanche photodiode (PerkinElmer) at National Center for Atmospheric Research (NCAR), Boulder, Colorado. The main focus of these tests was to examine the phototransistors’ performances by integrating them into the Raman-shifted Eye-safe Aerosol Lidar (REAL) operating at 1.543 micron. A simultaneous measurement of the atmospheric backscatter signals using the custom-built LPE-grown phototransistors and commercial APD demonstrated good agreement between these two devices. On the other hand, simultaneous detection of lidar backscatter signals using MBE-grown phototransistor and InGaAs APD, results showed somewhat agreement between these two devices with a longer tail of MBE-grown phototransistor. These custom-built phototransistors were optimized for detection around 2-μm wavelength and the lidar tests were performed at 1.543 μm. Phototransistor operations at 2-micron will improve the performance of a lidar system operating at that wavelength. Measurements include detecting ~14-km range hard targets (Rocky Mountains), atmospheric structure consisting of cirrus clouds and boundary layer. These phototransistors may have great potential for high sensitivity differential absorption lidar measurements of carbon dioxide and water vapor at 2.05-μm and 1.9-μm, respectively.