Structural and local electrical properties of AlInN/AlN/GaN heterostructures

GaN layers and Al_1−xIn_xN/AlN/GaN heterostructures have been studied by scanning probe microscopy methods. Threading dislocations (TDs), originating from the GaN (0 0 0 1) layer grown on sapphire, have been investigated. Using Current-Atomic Force Microscopy (C-AFM) TDs have been found to be highly conductive in both GaN and AlInN, while using semi-contact AFM (phase-imaging mode) indium segregation has been traced at TDs in AlInN/AlN/GaN heterostructures. It has been assessed that In segregation is responsible for high conductivity at dislocations in the examined heterostructures.     

高电子迁移率晶格匹配InAlN/GaN材料研究

文章基于蓝宝石衬底采用脉冲金属有机物化学气相淀积(MOCVD)法生长的高迁移率InAlN/GaN材料,其霍尔迁移率在室温和77 K下分别达到949和2032 cm²/Vs,材料中形成了二维电子气(2DEG). 进一步引入1.2 nm的AlN界面插入层形成InAlN/AlN/GaN结构,则霍尔迁移率在室温和77 K下分别上升到1437和5308 cm²/Vs. 分析样品的X射线衍射、原子力显微镜测试结果以及脉冲MOCVD生长方法的特点,发现InAlN/GaN材料的结晶质量较高,与GaN晶格匹配的InAlN材料具有平滑的表面和界面. InAlN/GaN和InAlN/AlN/GaN材料形成高迁移率特性的主要原因归结为形成了密度相对较低(1.6×10¹³-1.8×10¹³ cm^-2)的2DEG,高质量的InAlN晶体降低了组分不均匀分布引起的合金无序散射,以及2DEG所在界面的粗糙度较小,削弱了界面粗糙度散射. 关键词： InAlN/GaN 脉冲金属有机物化学气相淀积 二维电子气 迁移率     

Formation of high quality gallium nitride thin films on Ga-diffused Si(1 1 1) substrate

High quality gallium nitride thin films have been successfully grown on the Ga-diffused Si(1 1 1) substrates through ammoniating Ga₂O₃ thin films deposited by r.f. magnetron sputtering. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), atomic force microscope (AFM) and photoluminescence (PL) were used to characterize the synthesized samples. The analyses reveal that the formed films are high quality polycrystalline hexagonal gallium nitride. The as-formed GaN films show a flat surface topography with RMS roughness varied from 29 to 48 Å. The strong near-band-edge-emission peak around 368 nm was observed at room temperature. This is a novel method to fabricate GaN thin films based on the direct reaction between Ga₂O₃ and NH₃ on the Ga-diffused Si(1 1 1) substrates.     

Effect of thermal annealing on GaN pn-junction diode with Pt/Ag as ohmic contact

In this paper, the effect of thermal annealing on gallium nitride (GaN) pn-junction photodiode grown on Si(1?1?1) by RF-plasma assisted molecular beam epitaxy is described. Platinum (Pt) and silver (Ag) were used as ohmic contact for GaN pn-junction photodetector. The structural evolution and temperature dependence of the current of Pt/Ag contacts on GaN pn-junction at various annealing were investigated by scanning electron microscopy, atomic force microscopy, high resolution X-ray diffraction, and current–voltage (I–V) measurements, respectively. The temperature dependence of the current may be attributed to changes of the surface morphology and surface roughness of Pt/Ag contacts on the sample. The lower surface roughness was achieved at thermal annealing temperature of 700?°C.     

SrHf0.67Ti0.33O3 high-k films deposited on Si by pulsed laser deposition

Abstract: The large band gap (3.58?eV) and dielectric properties (?? _r =50) of bulk SrHf_0.67Ti_0.33O₃ (SHTO) make it a promising high-k material. SHTO films were deposited on p-type (100) Si single crystal substrates by pulsed laser deposition. The composition, structure, thickness, and roughness of the SHTO films have been studied using X-ray Photoelectron Spectroscopy, X-ray reflectivity, transmission electron microscopy, and atomic force microscopy. The capacitance?Cvoltage and leakage current density characteristics of the films have been evaluated. For a post-annealed SHTO film with a thickness of 25 nm, the relatively high permittivity of 35 was achieved with the low leakage current density of 4.96×10^?4?A/cm² at ?2?V bias voltage.     

Molecular beam epitaxy of GaN on a substrate of MoS2 layered compound

The feasibility of MoS₂ layered compound as a substrate for GaN growth was investigated. GaN films were successfully grown on MoS₂ by plasma-enhanced molecular beam epitaxy and the crystal quality of GaN on MoS₂ was compared with that on Al₂O₃. For GaN grown on MoS₂ substrate, it was found that the surface flatness observed by atomic force microscopy, stress in the film measured by Raman spectroscopy, optical properties measured by photoluminescence spectroscopy, and threading dislocation density observed by transmission electron microscopy show superior properties compared with that grown on Al₂O₃. These results suggest the layered compound such as MoS₂, which has no dangling bonds on the surface and has lattice mismatching of 0.9% to GaN, has high potential for a substrate of GaN growth. Received: 1 March 1999 / Accepted: 8 March 1999 / Published online: 26 May 1999     

Fabrication of aluminum nitride heterostructures on Si (1 1 1) substrate by plasma-assisted MBE

The aluminum nitride (AlN) heterostructures were successfully grown on silicon substrate by plasma-assisted molecular beam epitaxy. The surface morphology and structural and optical properties of the sample have been investigated by reflection high electron diffraction, scanning electron microscopy, field emission scanning electron microscopy (FESEM), energy dispersive X-ray, high-resolution X-ray diffraction (HR-XRD), Raman spectroscopy, and photoluminescence, respectively. HR-XRD measurement showed that the sample has a typical diffraction pattern of hexagonal AlN/GaN/AlN heterostructures. The Schottky characteristic of Pt contact on AlN/GaN/AlN heterostructures was also investigated under different annealing temperatures in nitrogen ambient. The temperature dependence and structural evolution of the Schottky barrier height (SBH) of Pt contacts were studied using the current–voltage measurement and FESEM, respectively. Our findings presented that the SBH of the samples change with different annealing temperatures.     

High temperature electron transport properties of AlGaN/GaN heterostructures with different Al-contents

Electron transport properties in AlGaN/GaN heterostructures with different Al-contents have been investigated from room temperature up to 680 K. The temperature dependencies of electron mobility have been systematically measured for the samples. The electron mobility at 680 K were measured as 154 and 182 cm²/V·s for Al_0.15Ga_0.85N/GaN and Al_0.40Ga_0.60N/GaN heterostructures, respectively. It was found that the electron mobility of low Al-content Al_0.15Ga_0.85N/GaN heterostructure was less than that of high Al-content Al_0.40Ga_0.60N/GaN heterostructure at high temperature of 680 K, which is different from that at room temperature. Detailed analysis showed that electron occupations in the first subband were 75% and 82% at 700 K for Al_0.15Ga_0.85N/GaN and Al_0.40Ga_0.60N/GaN heterostructures, respectively, and the two dimensional gas (2DEG) ratios in the whole electron system were 30% and near 60%, respectively. That indicated the 2DEG was better confined in the well, and was still dominant in the whole electron system for higher Al-content AlGaN/GaN heterostructure at 700 K, while lower one was not. Thus it had a higher electron mobility. So a higher Al-content AlGaN/GaN heterostructure is more suitable for high-temperature applications.     

MeV Al+ and Al2+ ions implantation in Si(100): surface roughness and defects in the bulk

This paper deals with the implantation of high-energy (1.0–3.0 MeV) atomic and molecular Al⁺ ions in Si(100) to a fluence of 5×10¹⁴ Al atoms/cm² at room temperature. The molecular effect, i.e. the increase of the displacement yield compared with the sum of the atomic yields, and the damage formation as well as defect behaviour after annealing have been investigated. A detailed experimental study has been made of the evolution of extended secondary defects which form during thermal anneals of Al⁺ or Al₂ ⁺ irradiated silicon. The samples have been examined using combined Rutherford backscattering and channeling experiments together with transmission electron microscopy observations. The surface structure of the implanted wafers has been measured by atomic force microscopy. The results for the implantation-induced roughness at the Si surface, resulting from Al⁺ or Al₂ ⁺ irradiation at the same energy/atom, total atomic fluence, flux rate, and irradiation temperature, are presented and discussed. Received: 19 August 1999 / Accepted: 20 October 1999 / Published online: 23 February 2000     

Improving Ni/GaN Schottky diode performance through interfacial passivation layer formed via ultraviolet/ozone treatment

Electrical passivation has a significant effect on metal-semiconductor (MS) device operations including performance and reliability. In this study, the improvement in performance of Ni/GaN Schottky diodes (SDs) through an ultraviolet/ozone (UV/O₃) interface treatment is investigated and the mechanism of carrier conduction at the MS junction interfaces is analyzed. The formation of surface oxide layer at the MS interface through the UV/O₃ treatment is confirmed by the measurements using X-ray photoelectron spectroscopy, contact angle, and atomic force microscopy. The atomic intensity and surface energy increased and surface roughness improved through the implementation of oxide layer. Electrical measurements reveal reduced leakage and improved breakdown voltage and are used to determine the Schottky barrier height and Richardson constant of the Ni/GaN MS SDs. The enhancement in the entire performance of the MS SDs is attributed to the passivation of defect centers at the dislocation-related pits through the formation of oxide layer with the UV/O₃ treatment, which thereby improves the carrier transfer properties of Ni/GaN SDs.