正十八硫醇钝化GaAs(100)表面特性研究

为了有效降低GaAs半导体表面态密度，提出了采用正十八硫醇（ODT，CH₃[CH₂]₁₇SH）进行GaAs表面钝化的方案。首先，分别对GaAs（100）晶片进行了常规硫代乙酰胺（TAM，CH₃CSNH₂）钝化和正十八硫醇钝化，通过X射线光电子能谱（XPS）对比分析了钝化前后晶片表面的化学成分，然后利用光致发光光谱（PL）对正十八硫醇处理的GaAs（100）晶片进行了钝化时间的优化，最后通过扫描电子显微镜（SEM）测试了钝化前后的晶片表面形貌。实验结果表明：采用正十八硫醇钝化的GaAs（100）表面，相比常规硫代乙酰胺钝化方案，具有更低的氧化物含量和更厚的硫化层厚度；室温钝化条件下，钝化时间越长，正十八硫醇的钝化效果越好，但PL强度在钝化超过24 h后基本达到稳定，最高PL强度提高了116%；正十八硫醇钝化的GaAs（100）晶片具有良好的表面形貌，表面形成了均匀、平整的硫化物钝化层。数据表明正十八硫醇是钝化GaAs（100）表面一种非常有效的技术手段。     

联氨溶液钝化GaAs(100)表面特性及其发光性能

为了有效降低GaAs表面态密度,获得稳定的高性能钝化膜,使用联氨溶液钝化GaAs(100)表面。通过光致发光对联氨溶液浓度、Na_2S浓度和钝化时间进行了优化。联氨溶液钝化后GaAs样品的PL比未处理的增加了1.22倍。采用X射线光电子能谱和原子力显微镜分析了联氨溶液钝化前后GaAs的表面成分和形貌。结果表明,联氨溶液钝化GaAs表面可以有效地去除表面氧化物,形成均匀、平整的GaN钝化层。通过表面稳定性测试发现,钝化后的GaAs表面在空气中放置数天,光致发光强度未见明显的退化(30 d内PL强度降低7%),说明钝化后GaAs表面的稳定性良好。     

中性(NH4)2S溶液钝化GaAs(100)表面的研究

采用同步辐射光电子能谱(SRPES)结合扫描电子显微镜(SEM)和称量法，研究了中性(NH₄)₂S溶液钝化GaAs(100)表面，并与常规(NH₄)₂S碱性溶液钝化方法进行了比较- SRPES结果表明该处理方法可以产生较厚的Ga硫化物层和较强的Ga—S键，Ga的硫化物有好的稳定性-称量法表明该方法有更低的腐蚀速率-SEM结果表明该方法钝化处理的GaAs表面所产生的腐蚀坑数目少，直径小- 关键词：     

CaAs(100)的(NH4)2Sx和P2S5/(NH4)2Sx表面钝化

利用光致发光谱、X射线光电子谱和俄歇电子谱等技术研究了(NH_4)_2S_x和P_2S_5/(NH_4)_2S_5化学钝化GaAs(100)表面.结果表明,(NH_4)_2S_x中S钝化可以完全去除GaAs表面的氧化物.P_2S_5/(NH_4)_2S_x中P_2S_5对降低G_2A_5表面态密度,提高光致发光强度是有效的.钝化表面P氧化物存在对防止GaAs表面初期氧化起重要作用. 关键词：     

GaAs(100)表面硫钝化的新方法:CH3CSNH2/NH4OH处理

建立了一种硫钝化GaAs(100)表面的新方法,即CH₃CSNH₂/NH₄OH溶液处理,应用同步辐射光电子能谱(SRPES)和X射线光电子能谱(XPS)表征了该钝化液处理的n-GaAs(100)表面的成键,特性和电子态.结果表明,经过处理的n-GaAs(100)表面,S既与As成键也与Ga成键,形成S与GaAs的新界面,并且Ga和As的氧化物被移走,这标志着CH₃CSNH₂/NH_{4关键词：}     

P2S5/NH4OH处理GaAs(100)表面的电子能谱研究

采用俄歇电子能谱(AES)和X射线光电子能谱(XPS)研究了P₂S₅/NH₄OH钝化液处理的GaAs(100)表面的微观特性。AES测量表明,在钝化膜和GaAs衬底之间的界面处无O组分,只有P和S组分。XPS测量分析指出,经过P₂S₅/NH₄OH溶液处理后,GaAs表面处Ga₂O₃和As₂O_{3关键词：}     

多种含硫溶液钝化(100)GaAs表面的实验研究

为实现GaAs表面的钝化,以Na2S、(NH4)2S、CH3CSNH2为主要研究对象,通过对比实验研究得出较为理想的湿法钝化液。通过光致发光(PL)谱研究了(NH4)2S 叔丁醇、CH3CSNH2 NH4OH、CH3CSNH2 叔丁醇三种不同含硫溶液钝化(100)GaAs表面后的发光特性。PL谱测试发现,(NH4)2S 叔丁醇饱和溶液处理过的(100)GaAs表面光致发光强度最强,PL谱的相对发光强度是未做钝化处理的10倍左右。因此得出(NH4)2S 叔丁醇饱和溶液是较为理想的(100)GaAs表面钝化液。     

CH3CSNH2钝化对铁磁金属与GaAs界面扩散的影响

通过实验对比,研究了CH₃CSNH₂钝化对铁磁金属与GaAs界面处As扩散行为的影响.发现S钝化处理改变了表面As元素的化学环境,减弱了As元素向铁磁金属外延层中的扩散现象,削弱了As与铁磁金属的反应,形成了较窄的反应层,并且改善了界面磁性.初步探讨了S钝化影响As扩散的原因. 关键词： S钝化 半导体界面 电子结构 磁性     

Co/S钝化GaAs(100)界面形成的SRPES研究

利用同步辐射光电发射谱研究了Co与CH\-3CSNH\-2处理的S钝化GaAs(100)的界面形成.发现 其界面反应较弱,Co覆盖层达到0.8nm时,形成稳定的界面.GaAs表面上和S原子形成桥 键的Ga原子与Co发生交换反应并扩散到覆盖层中,形成Co—S键.Co覆盖层表面无偏析As的出现,与Co/GaAs(100)界面不同,这表明GaAs表面的S钝化可有效地阻止As原子向覆盖层的扩散. 关键词：     

InAs/GaAs柱形岛的制备及特性研究

利用固源分子束外延（MBE）的方法经SK模式自组装生长由多层InAs／GaAs量子点组成的柱形岛.具体分析了GaAs间隔层厚度，生长停顿时间以及InAs淀积量对发光峰波长的影响.原子力显微镜（AFM）结果显示柱形岛表面的形状和尺寸都比较均匀；室温下不同高度的柱形岛样品的发光波长分别达到1.32和1.4μm，而单层量子点的发光波长仅为1.1μm，充分说明了量子点高度对发光波长的决定性影响，这为调节量子点发光波长提供了一种直观且行之有效的方法. 关键词： 柱形岛 生长停顿 间隔层厚度 PL谱     

PASSIVATION OF THE InP(100) SURFACE USING (NH4)2Sx

InP(100) surface treated with (NH₄)₂S_x has been investigated by using photolumines-cence(PL), Auger electron spectroscopy and X-ray photoelectron spectroscopy, It is found that PL intensity increased by a factor of 3.3 after (NH₄)₂S_x passivation and the sulfur remained on the surface only bonded to indium, not to phosphorus. This suggests that the sulfur atoms replace the phosphorus atoms on the surface and occupy the phosphorus vacancies.     

Surface reactions in atomic layer deposition of HfO2, ZrO2 and Al2O3 on hydroxylated and sulfur-passivated GaAs(1 0 0) surfaces: A comparative study by density functional theory

The surface reactions in atomic layer deposition (ALD) of HfO₂, ZrO₂ and Al₂O₃ on hydroxylated and sulfur-passivated GaAs surfaces are compared by using density functional theory. The HfCl₄ and ZrCl₄ half-reactions show large similarities in energetics and geometrical structure. However, both of them show large discrepancies with the Al(CH₃)₃ (TMA) half-reaction. Calculations find that it is more energetically favorable for the Al₂O₃ deposition than the HfO₂ and ZrO₂ deposition at the initial ALD stage. In addition, calculations find that although the GaAs passivation with sulfur helps to improve the interfacial properties, it is both kinetically and thermodynamically less favorable.     

Origin of HfO2/GaAs interface states and interface passivation: A first principles study

First principles calculations of HfO₂/GaAs interfaces indicate that the interface states originate from the charge mismatch between HfO₂ and GaAs surfaces. We find that a model neutral interface (HfO₂ and GaAs surfaces terminated with two O and one Ga atoms per surface unit cell) removes gap states due to the balance of the interface charge. F and H can neutralize the HfO₂/GaAs interface resulting in useful band offsets, thus becoming possible candidates to passivate the interface states.     

XPS analysis of surface chemistry of near surface region of epiready GaAs(1 0 0) surface treated with (NH4)2Sx solution

In this work we analyze the effect of (NH)₂S_x wet treatment on the GaAs(1 0 0) covered with “epiready” oxide layer without any pretreatment in order to check the removal of oxides and carbon-related contamination, and the formation of sulfur species. The sulfidation procedure consisted of epiready sample dipping (at room and 40 °C temperatures) in an ammonium polysulfide solution combined with a UHV flash annealing up to 500 °C.The inspection of the XPS As 2p_3/2 and Ga 2p_3/2 spectra taken at surface sensitive mode revealed: (i) the temperature-dependent reduction of the amount of GaAs oxides and carbon contamination after sulfidation, and almost their complete removal after subsequent annealing, (ii) the creation of sulfur bonds with both Ga and As, with more thermally stable Ga-S bonds, and (iii) the slight reduction in elemental arsenic amount.     

Surface electronic properties of sulfur-treated GaAs determined by surface photovoltage measurement and its computer simulation

The Kelvin method together with the simulations of surface photovoltage has been used to determine the surface electronic properties, i.e. the surface band bending (qV_S), surface state density (N_SS0) and surface fixed charge (Q_Fx) of S₂Cl₂-treated GaAs (100) surfaces. The measured values of surface photovoltage (SPV) do not show saturation at high photon flux densities in contradiction to the simple theory of SPV. This behavior of SPV agrees very well with the rigorous computer simulations and can be explained in terms of the Dember effect. Moreover, the SPV values become insensitive to surface states at moderate photon flux densities. On this basis, the surface band bending of untreated (0.79 eV) and S₂Cl₂-treated (0.60 eV) GaAs surfaces was determined. The band diagrams summarizing the obtained results proved the influence on the potential variations not only from the ionized surface states and surface fixed charge but also from the surface dipole layer on the S₂Cl₂-treated GaAs surface. The dipole arises most probably due to the S-Ga bonding on the surface. The presented results offer an alternative explanation for increased PL commonly observed after the sulfidation in the absence of substantial reduction in the band bending.     

The surface of TiO2 gate of 2DEG-FET in contact with electrolytes for bio sensing use

In order to apply two-dimensional electron-gas-field-effect-transistors (2DEG-FETs) for cell-viability sensors, we investigated the chemical/electrical properties of TiO₂ thin films (13-17 nm) prepared with the sol-gel technique on the gate surface of AlGaAs/GaAs 2DEG-FETs. Photochemical/electrochemical reactions on GaAs surface in electrolytes, which induce the degradation of 2DEG-FET performance, are effectively suppressed by introducing a TiO₂ thin film on the gate area of 2DEG-FETs. Compared to conventional ion-selective FETs (ISFETs), the TiO₂/2DEG-FETs in this study exhibit a high sensitivity (410 mV/mM) for H₂O₂ detection. TiO₂ surfaces show better biocompatibility than GaAs surfaces as demonstrated by direct cell culture on these surfaces.     

Morphology and optical properties of p-type porous GaAs(1 0 0) layers made by electrochemical etching

Porous GaAs layers were formed by electrochemical etching of p-type GaAs(1 0 0) substrates in HF solution. A surface characterization has been performed on p-type GaAs samples using X-ray photoelectron spectroscopy (XPS) technique in order to get information about the chemical composition, particularly on the surface contamination. According to the XPS spectra, the oxide layer on as-received porous GaAs substrates contains As₂O₃, As₂O₅ and Ga₂O₃. Large amount of oxygen is present at the surface before the surface cleaning.Compared to untreated GaAs surface, room temperature photoluminescence (PL) investigations of the porous layers reveal the presence of two PL bands: a PL peak at ∼871 nm and a “visible” PL peak at ∼650-680 nm. Both peak wavelengths and intensities varied from sample to sample depending on the treatment that the samples have undergone. The short PL wavelength at 650-680 nm of the porous layers is attributed to quantum confinement effects in GaAs nano-crystallites. The surface morphology of porous GaAs has been studied using atomic force microscopy (AFM). Nano-sized crystallites were observed on the porous GaAs surface. An estimation of the mean size of the GaAs nano-crystals obtained from effective mass theory and based on PL data was close to the lowest value obtained from the AFM results.