Atomic-layer Deposition for Improved Performance of III-N Avalanche Photodiodes
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Atomic-layer Deposition for Improved Performance of III-N Avalanche Photodiodes John Hennessy1, L. Douglas Bell1, Shouleh Nikzad1, Puneet Suvarna2, Jeffrey M. Leathersich2, Jonathan Marini2, F. (Shadi) Shahedipour-Sandvik2 1 2
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA College of Nanoscale Science and Engineering, State University of New York, Albany, NY
ABSTRACT We have investigated surface modification methods for avalanche photodiodes using dielectrics deposited by atomic layer deposition (ALD). Arrays of mesa GaN APDs were fabricated, and ALD Al2O3 was used for sidewall passivation prior to completing the APD array. The use of ALD Al2O3 in this manner was observed to result in a large average improvement in APD dark current when compared with devices using more conventional SiO2 passivation layers produced by chemical vapor deposition. Co-processed metal-oxide-semiconductor (MOS) capacitors fabricated with the same passivation layers show significant improvement in electrical interface quality for devices with ALD Al2O3. INTRODUCTION Avalanche photodiodes (APDs) are an attractive replacement for conventional high-gain UV detectors such as photomultiplier tubes or photocathode/microchannel plate systems. These devices have important applications for sensor systems which must detect an ultraviolet signal in the presence of a large visible background. Due to the bulk, fragility, cost, and high-voltage requirements of conventional technologies, an all-solid-state alternative is highly desirable. III-N avalanche APDs are one candidate for next-generation UV detectors. Due to the wide band-gap of AlGaN materials, visible and solar-blind operation of detectors and imagers can be achieved. Visible-blind detectors are important in both astronomical and terrestrial settings. However, materials challenges remain in order for III-N APDs to replace conventional technologies. Material quality and surface passivation strongly affect the contribution of undesirable current components such as those produced by defect-related microplasmas [1,2]. In order to achieve material-limited operation, surface properties must be optimized. These surface properties are typically addressed in mesa-isolated diodes through the use of a deposited sidewall passivation layer. In reported work on GaN mesa diodes the conventional material choice is often SiO2 deposited via chemical vapor deposition [3-5]. Previous surface passivation studies in the GaN/AlGaN material system have noted the beneficial nature of ALD Al2O3 in HFET devices [6], inversion-channel MOSFETs [7], and LEDs [8]. In this work we extended this ALD approach to the surface passivation of GaN mesa APDs. ALD is an attractive option for III-N sidewall passivation due to the ease in depositing potentially more compatible materials such as Al2O3 and AlxNy, as well the ability to conformally coat three dimensional structures like mesa diodes.
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EXPERIMENTAL DETAILS The starting substrates used in this experiment were grown by metal-organic chemical
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