Ultrasensitive and high-speed AlGaN/AlN solar-blind ultraviolet photodetector: a full-channel-self-depleted phototransistor by a virtual photogate
Jiabing Lu, Zesheng Lv, Xinjia Qiu, Shiquan Lai, Hao Jiang
Abstract
High sensitivity, high solar rejection ratio, and fast response are essential characteristics for most practical applications of solar-blind ultraviolet (UV) detectors. These features, however, usually require a complex device structure, complicated process, and high operating voltage. Herein, a simply structured n-AlGaN/AlN phototransistor with a self-depleted full channel is reported. The self-depletion of the highly conductive n-AlGaN channel is achieved by exploiting the strong polarization-induced electric field therein to act as a virtual photogate. The resulting two-terminal detectors with interdigital Ohmic electrodes exhibit an ultrahigh gain of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m1"> <mml:mrow> <mml:mn>1.3</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>5</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> , an ultrafast response speed with rise/decay times of 537.5 ps/3.1 μs, and an ultrahigh Johnson and shot noise (flicker noise) limited specific detectivity of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m2"> <mml:mrow> <mml:mn>1.5</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>18</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m3"> <mml:mrow> <mml:mn>4.7</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mrow> <mml:mn>16</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> ) Jones at 20-V bias. Also, a very low dark current of the order of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m4"> <mml:mrow> <mml:mo form="prefix">∼</mml:mo> <mml:mi>pA</mml:mi> </mml:mrow> </mml:math> and a photo-to-dark current ratio of above <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m5"> <mml:mrow> <mml:msup> <mml:mrow> <mml:mn>10</mml:mn> </mml:mrow> <mml:mn>8</mml:mn> </mml:msup> </mml:mrow> </mml:math> are obtained, due to the complete depletion of the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline" id="m6"> <mml:mrow> <mml:mi mathvariant="normal">n</mml:mi> <mml:mtext>-</mml:mtext> <mml:msub> <mml:mrow> <mml:mi>Al</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0.5</mml:mn> </mml:mrow> </mml:msub> <mml:msub> <mml:mrow> <mml:mi>Ga</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>0.5</mml:mn> </mml:mrow> </mml:msub> <mml:mi mathvariant="normal">N</mml:mi> </mml:mrow> </mml:math> channel layer and the high optical gain. The proposed planar phototransistor combines fabrication simplicity and performance advantages, and thus is promising in a variety of UV detection applications.