Present Status of III-Nitride Based Photodetectors
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Present Status of III-Nitride Based Photodetectors Eva Monroy1, Fernando Calle1, José Luis Pau1, Elías Muñoz1, Franck Omnès2, Bernard Beaumont2, and Pierre Gibart2 1 Dpto. Ingeniería Electrónica, ETSI Telecomunicación, Universidad Politécnica de Madrid, Ciudad Universitaria, 28040-Madrid, Spain. 2 CRHEA-CNRS, Rue Bernard Gregory, Parc Sophia Antipolis, 06560-Valbonne, France. ABSTRACT This paper describes the characteristics of a variety of AlGaN-based photodetectors (photoconductors, metal-semiconductor-metal photodiodes, Schottky photodiodes and p-i-n photodiodes), grown on sapphire by metalorganic vapor phase epitaxy. The features that determine their performance are analyzed. Results using other substrates (epitaxial lateral overgrown GaN, Si) are also presented.
INTRODUCTION UV photodetection has drawn a great deal of attention in the recent years [1]. Both civil and military industries demand better UV instrumentation, for applications such as engine control, solar UV monitoring, source calibration, UV astronomy, flame sensors, detection of missile plumes, and secure space-to-space communications. Wide-bandgap compounds are the best choice for UV detectors, since they combine the advantages of compact, low-bias, semiconductor devices, with their intrinsic visible-blindness and higher stability. III-Nitrides (AlN, GaN, and InN) present some advantages over other wide-bandgap semiconductors [2,3], such as high absorption coefficients and sharper cutoffs, due to their direct bandgap, the possibility of selecting the cutoff wavelength by changing the mole fraction of their ternary alloys, and their capability for heterojunction devices. In this work, we summarize our recent achievements in AlGaN-based UV photodetectors, (photoconductors, Schottky barrier detectors, metal-semiconductor-metal photodiodes, and p-n junction photodiodes), analyzing the main features of the different devices. The effect of material quality is also discussed.
EXPERIMENTAL Different types of photodetector structures have been characterized: photoconductors, metalsemiconductor-metal (MSM) photodiodes, Schottky barrier photodetectors, and p-i-n photodiodes. The devices were fabricated on AlGaN epitaxial layers grown on sapphire by metalorganic vapor phase epitaxy [4]. Their schematic structures are shown in figure 1.
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Figure 1. Schematic structure of (a) AlGaN photoconductors, (b) MSM photodiodes, (c) Schottky barrier photodetectors, and (d) p-i-n photodiodes. The value of the responsivity and its dependence on the incident power have been measured using non-focused continuous-wave laser lines: He-Cd (325 nm) and Ar+ (257 nm). Spectral responsivity studies were performed with a 150 W Xenon arc lamp and a Jobin-Yvon H-25 monochromator. The optical system was calibrated by means of a pyroelectric detector. The time response of the detectors was measured using the fourth frequency of a Nd-YAG laser (266 nm), with 10 ns Gaussian pulses. Devices under test were connected in series with a load resistance, and the vo
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