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Highly sensitive and fast imaging at short-wavelength infrared (SWIR) is one of the key enabling technologies for the direct-imaging of habitable exoplanets. SWIR imaging systems currently available in the market are dominated by imagers based on InGaAs PIN photodiodes. The sensitivity of these cameras is limited by their read-out noise (RON) level. Sensors with internal gain can suppress the RON and achieve lower noise imaging. In this paper, we demonstrate a SWIR camera based on 3D-engineered InP/InGaAs heterojunction phototransistors with responsivities around 2000 A/W which provides a shot-noise limited imaging sensitivity at a very low light level. We present the details of the semiconductor structure, the microfabrication, and the heterogeneous integration of this camera. The low capacitance pixels of the imager achieve 36 electron effective RON at frame rates around 5 kilo-frames per second at an operating temperature of 220 K and a bias voltage of 1.1 V. This is a significant step toward achieving highly sensitive imaging at SWIR at high frame rates and noncryogenic operating temperatures. Based on the proposed modeling and experimental results, a clear path to reach the RON less than 10 electrons is presented. [ABSTRACT FROM AUTHOR]

We discuss the light absorption enhancement factor dependence on the design of nanogratings inscribed into metal-semiconductor-metal photodetector (MSM-PD) structures. These devices are optimized geometrically, leading to light absorption improvement through plasmon-assisted effects. Finite-difference time-domain (FDTD) simulation results show ~50 times light absorption enhancement for 850 nm light due to improved optical signal propagation through the nanogratings. Also, we show that the light absorption enhancement is strongly dependent on the nanograting shapes in MSM-PDs. [ABSTRACT FROM AUTHOR]

The finite difference time-domain (FDTD) method is used to simulate the light absorption enhancement in a plasmonic metalsemiconductor- metal photodetector (MSM-PD) structure employing a metal nanograting with phase shifts. The metal fingers of the MSM-PDs are etched at appropriate depths to maximize light absorption through plasmonic effects into a subwavelength aperture. We also analyse the nano-grating phase shift and groove profiles obtained typically in our experiments using focused ion beam milling and atomic force microscopy and discuss the dependency of light absorption enhancement on the nano-gratings phase shift and groove profiles inscribed intoMSM-PDs. Our simulation results show that the nano-grating phase shift blue-shifts the wavelength at which the light absorption enhancement is maximum, and that the combined effects of the nano-grating groove shape and phase shift degrade the light absorption enhancement by up to 50%. [ABSTRACT FROM AUTHOR]

The characterization and analysis of high frequency noise of InP-based high electron mobility transistors in the impact ionization regime reveal that different physical mechanisms are responsible for the excess channel noise at different frequency ranges. The excess noise at frequencies below 10 GHz is mainly due to the hole recombination in the channel. However, excess channel noise at higher frequencies could be dominated by the fluctuation of impact ionization which has a much smaller time constant and therefore a much higher cutoff frequency. [ABSTRACT FROM AUTHOR]