In-Plane Anisotropic Photoconduction in Nonpolar Epitaxial a-Plane GaN

Abstract

Nonpolar a-plane GaN epitaxial films were grown on an r-plane sapphire using the plasma-assisted molecular beam epitaxy system, with various nitrogen plasma power conditions. The crystallinity of the films was characterized by high-resolution X-ray diffraction and reciprocal space mapping. Using the X-ray "rocking curve-phi scan", [0002], [1-100], and [1-102] azimuth angles were identified, and interdigitated electrodes along these directions were fabricated to evaluate the direction-dependent UV photoresponses. UV responsivity ( R) and internal gain ( G) were found to be dependent on the azimuth angle and in the order of [0002] > [1-102] > [1-100], which has been attributed to the enhanced crystallinity and lowest defect density along [0002] azimuth. The temporal response was very stable irrespective of growth conditions and azimuth angles. Importantly, response time, responsivity, and internal gain were 210 ms, 1.88 A W, and 648.9%, respectively, even at a bias as low as 1 V. The results were validated using the Silvaco Atlas device simulator, and experimental observations were consistent with simulated results. Overall, the photoresponse is dependent on azimuth angles and requires further optimization, especially for materials with in-plane crystal anisotropy.

Photodetection Properties of Nonpolar a‐Plane GaN Grown by Three Approaches Using Plasma‐Assisted Molecular Beam Epitaxy

“…Figure represents the relationship between average values of the FWHM of all the samples with respect to the sensitivity and responsivity as taken from Table S4, Supporting Information. As FWHM is directly proportional to the defect density, it can be understood that the higher the FWHM, higher will be the defect density and the corresponding sensitivity of the PDs should be low. The defects in the film act as recombination centers, thereby reducing the overall efficiency of the device.…”

“…Based on the materials used, device type, and electrodes structure, these detectors can be categorized as metal–semiconductor–metal (MSM), Schottky barrier, nanostructures, multi‐quantum well (MQW), and hybrid structures, etc . Among these detectors, back to back Schottky MSM type detectors have the advantage of very low dark current due to the rectifying nature of the contacts, reduced parasitic capacitance, low noise, large internal gain, simple fabrication process steps, and also huge commercial throughput . The MSM structure consists of two symmetrical electrodes deposited on the semiconductor material, which can be either Ohmic or Schottky.…”

“…[7][8][9] Among these detectors, back to back Schottky MSM type detectors have the advantage of very low dark current due to the rectifying nature of the contacts, reduced parasitic capacitance, low noise, large internal gain, simple fabrication process steps, and also huge commercial throughput. [2,8,[10][11][12] The MSM structure consists of two symmetrical electrodes deposited on the semiconductor material, which can be either Ohmic or Schottky. An external bias applied to the Schottky type of electrodes results in one electrode in forward and another in reverse bias and facilitates the flow of photogenerated electrons.…”

ZnO‐Based Ultraviolet Photodetectors with Tunable Spectral Responses

“…In 2018, Wang et al fabricated GaN‐based UV photodetectors via metal‐organic chemical vapor deposition (MOCVD) with a low dark current of 1.3 nA at 2 V, while the ratio of photocurrent ( I ph ) to dark current ( I d ) was only 2 . In addition, commercial growth methods of GaN semiconductor, such as MOCVD and molecular beam epitaxy (MBE), are expensive and always require high growth temperatures. In 2018, Sun et al reported a flexible type of SiC nanowire UV detectors with both rise and decay times less than 30 ms .…”

“…In 2018, Wang et al fabricated GaNbased UV photodetectors via metal-organic chemical vapor deposition (MOCVD) with a low dark current of 1.3 nA at 2 V, while the ratio of photocurrent (I ph ) to dark current (I d ) was only 2. [10] In addition, commercial growth methods of GaN semiconductor, such as MOCVD and molecular beam epitaxy (MBE), [11][12][13] are expensive and always require high growth temperatures. In 2018, Sun et al reported a flexible type of SiC nanowire UV detectors with both rise and decay times less than 30 ms. [14] However, such devices exhibited only a extremely tiny photocurrent of 11 pA at 5 V under an illumination density of 10 mW cm À2 , which is particularly susceptible to external interference, limiting the practical applications.…”