Characterization and Modeling of Photoconductive GaN Ultraviolet Detectors

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 10 3 A/W have been measured for an incident power of lW/m 2 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.

Electrical and Photoelectronic Properties of Hexagonal GaN

“…From frequency dependent measurements a stationary PC lifetime of 16 ms was obtained in agreement with previous results [4,7]. For low incident power the PC varies with excitation intensity (P) as expected like % P À0X9 [9]. In the photoquenched PC spectrum (Fig.…”

Visible-blindness in photoconductive and photovoltaic AlGaN ultraviolet detectors

“…When the light is removed, the excess of carriers is captured by the traps in dislocations. This very slow process is the origin of the PPC effects observed in this material, [17][18][19]25 since electrons have to cross a potential barrier that separates them from their recombination centers. Spatial separation of carriers have also been proposed as the origin of PPC in other semiconductors.…”

“…18,27 In contrast, photoconductors show a clearly sublinear dependence, which was already reported. 17,25 These behaviors were checked in GaN detectors to be independent of the excitation wavelength, either above or below the bandgap.…”

“…[16][17][18] However, this responsivity decreases with optical power approximately as P -0.9 , and is also strongly temperature dependent. DC spectral response shows a quite poor UV/visible contrast, which hardly reaches 100.…”

Photoconductivity in AlxGa1—xN with Different Al Contents

“…Key issues are fast response times and a high contrast between intrinsic (above band gap) and extrinsic (below band gap) response. In GaN and AlGaN based photoconductors prolonged non-exponentional conductivity decay after exposure with above or below band gap light has been commonly found [1,2,8,10,11]. In this paper, we compare n-and p-type GaN as well as n-type AlGaN with respect to spectral and transient responsivity at 300 and 500 K.…”