Abstract Body: Gallium nitride (GaN) with bandgap energy of 3.4 eV with a high breakdown electric field (~3.3 MV/cm) is useful for ultraviolet (UV) optical detectors. Since GaN avalanche photodiodes (APDs) have a high sensitivity and capability of operation in the visible-blind region with high optical gain with low dark current, UV-APD arrays are considerably well-suited for many applications in UV imaging systems, astronomy, military systems, and bio-aerosol detection to improve the collection efficiency and sensitivity for low-level light detection. Achieving the high crystalline quality of epitaxial layer structures with reduced-defect densities as well as optimizing the fabrication processes will significantly improve GaN APD arrays to achieve a high pixel yield and uniform breakdown voltage with low leakage current. Evaluation of these 6x6 arrays will help to confirm the uniformity of the epitaxial materials and device processing as well. In this work, visible-blind front-illuminated GaN p-i-n APDs were grown by metalorganic chemical vapor deposition (MOCVD) on 25 mm dia. bulk Ammono® n-GaN substrates having a low etch pit density (EPD) less than 5 × 104 [cm-2] and processed into 6x6 APD arrays. The MOCVD growth was performed in a close-coupled-showerhead AIXTRON 6x2” MOCVD system and employed trimethylgallium and NH3 as primary precursors and SiH4, and Cp2Mg as dopants. X-ray diffraction (XRD) was used for the characterization of the crystallographic quality of the APD structure. The full widths at half maximum of the rocking curve derived from (0.02) and (1.02) diffraction exhibit values of 73 and 41 arc-sec, respectively, primarily determined by the properties of the GaN substrate. Hall-effect characterization was used for the measurement of the electrical properties of the doped layers including the free-carrier concentration, mobility, and resistivity. The epitaxial layers grown on the GaN substrates include a 1.0 μm thick n-GaN:Si layer (n~7×1018 cm-3), 0.2 μm thick u-GaN undoped layer, 0.1 μm thick p-GaN:Mg layer (p~6x1017 cm-3) and 0.02 μm thick p++-GaN:Mg layer for a target breakdown voltage of 80 V. The surface morphology of the GaN p-i-n UV-APD epitaxial structures were studied by atomic force microscopy (AFM). The corresponding root-mean-square (RMS) values for scanning area of 5×5 μm2 for GaN/sapphire u-GaN template and n-GaN substrate are 0.15 nm and 0.07 nm respectively for the typical case. To confirm the doping profile of the layers, secondary ion mass spectrometry (SIMS) measurements were performed. The as-grown wafers were processed using ion-implantation isolation into 6x6 APD arrays having 60 µm-dia. pixels. The reverse-biased J-V characteristics of the GaN APD arrays under dark and 355 nm illumination conditions have been measured at 300K. The dark current density is 10-9 A/cm2 at reverse bias up to -20 V and breakdown voltage of 80 ± 1 V for all 36 devices which confirms a high uniformity of growth and fabrication processes. The maximum avalanche gain reached 3 × 105 at the breakdown. The details of growth, characterization, and fabrication processes as well as further device data will be discussed in the presentation. Work supported in part by US Army Research Office under W911NF-15-1-0489, administered by M. Gerhold, by the US Department of Energy under DESC0019133, and NASA under 80NSSC18C0093. This work was performed in part in the facilities of the Georgia Tech Institute for Electronics and Nanotechnology, a member of the National Nanotechnology Coordinated Infrastructure, which is supported by the National Science Foundation (Grant ECCS-154217). The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either express or implied, of DoE, ARO, or the U.S. Government.

Growth and Characterization of p-i-n GaN UV 6 × 6 Avalanche Photodiodes Arrays with Large Detection Area

II: Group III-Nitride Photodetectors

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Growth and Characterization of p-i-n GaN UV 6 × 6 Avalanche Photodiodes Arrays with Large Detection Area

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