First observation of electronic trap levels in freestanding GaN crystals extracted from Si substrates by hydride vapour phase epitaxy

Abstract

The electronic deep level states of defects embedded in freestanding GaN crystals exfoliated from Si substrates by hydride vapour phase epitaxy (HVPE) is investigated for the first time, using deep level transient spectroscopy (DLTS). The electron traps are positioned 0.24 eV (E1) and 1.06 eV (E2) below the conduction band edge, respectively. The capture cross sections of E1 and E2 are evaluated to be 1.65 × 10 −17 cm 2 and 1.76 × 10 −14 cm 2 and the corresponding trap densities are 1.07 × 10 14 cm −3 and 2.19 × 10 15 cm −3 , respectively. The DLTS signal and concentration of the electronic deep levels are independent of the filling pulse width, and the depth toward the bottom of the sample, evidenced by the fact that they are correlated to noninteracting point defects. Furthermore, Photoluminescence (PL) measurement shows green luminescence, suggesting that unidentified point defects or complex, which affect the optical characterisitics, exhibit. Despite the Si-based materials, the freestanding GaN exhibits deep level characteristics comparable to those of conventional freestanding GaN, suggesting that it is a desirable material for use in the next generation optoelectronic devices with the large-scalibilityand low production costs.

Deep Level Transient Fourier Spectroscopy (DLTFS) and Isothermal Transient Spectroscopy (ITS) in vertical GaN-on-GaN Schottky barrier diodes

“…5. The trap density (NT) for T1 and T2 is computed from the DLTFS transient signal magnitude (ΔC) by using the following expression [7,18] ( 16) where CR is the quiescent reverse bias capacitance VQR = -5 V, and ND is the effective doping concentration (2×10 16 cm -3 ) in the GaN layer. The calculated trap concentration (NT) for T1 and T2 is about 3.8×10 13 cm -3 and 8×10 14 cm -3 , respectively.…”

“…Several authors used the conventional deep level transient spectroscopy (DLTS) to identify the electrically active traps in vertical GaN-on-GaN SBDs [8][9][10][11][12][13][14][15][16]. The boxcar (rate-window concept) and lock-in (square wave weighting function) methods were used to compute the trap parameters through maximum temperature analysis of the DLTS curve [5][6][7].…”

Current Transport Mechanism in Palladium Schottky Contact on Si-Based Freestanding GaN

“…InGaN/GaN multi-quantum well (MQW) light-emitting diodes (LEDs) with a large scalability and a desirable production cost [13][14][15][16].…”

“…However, challenges such as size limits (<6 inch diameter) and manufacturing expenditure have restricted the successful introduction of HVPE freestanding GaN wafers into the commercial community [12]. Recently, we realized Si-based homoepitaxial InGaN/GaN multi-quantum well (MQW) light-emitting diodes (LEDs) with a large scalability and a desirable production cost [13][14][15][16].…”

Research Progress of ScAlMgO4 Crystal: a Novel GaN and ZnO Substrate

“…由于日益增长的能源电力需求，人们对电力转 换的效率要求越来越高，各国开始紧密出台半导体 产业的相关政策，第三代半导体的发展更是被抬到 一个前所未有的高度 [1] 。不同于以 Si、Ge 为代表的 第一代半导体材料和以 GaAs、InP 为代表的第二代 III-V 族半导体材料，第三代半导体具有更大的禁带 宽度(通常大于 2.3 eV)，更低的开关损耗，从而可 以实现更高效的能量转换。作为第三代半导体的核 心支撑材料，氮化镓(Gallium nitride，GaN)和氧化 锌(Zinc oxide，ZnO)在 PN 结二极管、肖特基势垒 二极管、高电子迁移率晶体管、蓝紫光固体激光器、 光导开关器件、核探测器件等领域有着广泛的应用 [2] 。目前 GaN 基与 ZnO 基器件的发展主要是在 Si、 蓝宝石等异质衬底上外延得到，由于衬底与外延层 之间存在较大的晶格失配与热失配，导致器件内部 产生大量缺陷、位错，进而引起阈值电压不稳定、 电流崩塌等问题，进一步降低器件的使用寿命和稳 定性 [3][4] 。因此寻找新型理想衬底材料对于以 GaN 和 ZnO 为主的第三代半导体器件的发展十分重要。 ScAlMgO4(Scandium magnesium aluminate, SCAM)作为多组分氧化物其中的一种，其熔点为 2173 K。上世纪九十年代，因 SCAM 与 GaN [1000] 方向晶格失配率约为 1.4 %，作为衬底材料开始为 人们熟知 [5] ；随后，又因其与 ZnO 具有很高的晶格 匹配度([1000]方向晶格失配比为 0.09 % [6] )，被认为 是一种理想的高质量异质外延衬底材料。除了单晶 衬底，SCAM 薄膜通常被用作 GaN 与 ZnO 薄膜外 延的缓冲层 [7][8] 。在带电粒子探测方面，较重的金 属元素对背景中的 X 射线与 γ 射线具有较高的吸收， 较轻的元素对背景中的中子具有较高的灵敏度， SCAM 因含有中间原子序数范围的元素，可用于带 电粒子的闪烁探测器 [9] 。为解决目前白光 LED 出现 的色彩还原性差、显色指数低、发光波段单一，以 及寿命短、光通量和光效率低、成本高等问题，亟 需一种新型荧光衬底材料。相较于传统 GaN 衬底材 料，SCAM 属 于多 元氧化 物，包含 Sc 3+ 、Al 3+ 、…”