Characterization and Modeling of Photoconductive GaN Ultraviolet Detectors
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Internet Journal o f
Nitride S emiconductor Research
Volume 2, Article 12
Characterization and Modeling of Photoconductive GaN Ultraviolet Detectors E. Monroy, J. A. Garrido, E. Muñoz, I. Izpura, F. J. Sánchez, M. A. Sánchez-García, E. Calleja Dpt. Ingeniería Electrónica, E.T.S.I. Telecomunicación, Politécnica, Ciudad Universitaria B. Beaumont, Pierre Gibart Centre de Recherche sur l'Hetero-Epitaxie et ses Applications, CRHEA-CNRS This article was received on June 9, 1997 and accepted on July 10, 1997.
Abstract In this work high gain GaN photoconductive UV detectors have been fabricated and characterized, and a novel gain mechanism, dominant in these detectors, is described. DC responsivities higher than 103A/W have been measured for an incident power of lW/m2 at room temperature. The photoconductive gain depends directly on the bias voltage and scales with incident power as P-k (k ≈ 0.9) for more than five decades. A decrease of both gain and k parameter with temperature has also been observed. As a consequence of the slow non-exponential transient response, AC gain measurements result in lower values for gain and k parameter, which are frequency dependent. The high responsivity, non-linear behavior and slow non-exponential transient response, are all modeled taking into account a modulation mechanism of the layer conductive volume. Such spatial modulation is due to the photovoltaic response of the potential barriers related to the surface and charged dislocations arrays.
1. Introduction Considering current advances in nitride technology, GaN is the most promising semiconductor for photodetection in the ultraviolet (UV) region of the spectrum [1]. Its direct wide bandgap makes it suitable to develop efficient visible blind sensors [2]. Taking into account its superior radiation hardness and high temperature resistance, this material is suitable for devices working in extreme conditions. Moreover, the Alx Ga x-1N system should enable to develop UV detectors with a cut-off wavelength tunable from 366nm to 200nm [3] [4]. Applications range from space communications to ozone layer monitoring or flame detection. Photocoductive GaN detectors have early attracted a significant interest [5] [6] [7] [8] [9]. For their simplicity, they are candidates as low cost UV detectors in consumer and environmental applications. Their high responsivity would enable their use without any preamplifier stage. Some of the characteristics of GaN photoconductors have been reported. There is a general agreement on the presence of an abnormally high responsivity [5] [6] [9] and persistent photoconductivity [7] [10] [11], which have been tentatively attributed either to deep levels [9] or to Mg-doping related centers [8]. A frequency dependence of the responsivity has also been detected [7] [11]. Reported data also indicate a very non-linear behavior, with a photoconductive gain decreasing with the optical power [5] [7]. In this work we present a study of the physical mechanism of photoconductive gain in GaN epitaxial layers, and the comp
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