Doping of molecular beam epitaxy HgCdTe using an arsenic cracker source (As2)

This study investigated the incorporation of arsenic dimers (As₂), delivered from a “cracker” effusion cell. The HgCdTe epilayers were deposited under standard growth conditions. During deposition, arsenic was incorporated using both a standard arsenic effusion cell and a cracker cell. It was found that arsenic concentration rose dramatically as a function of cracker-zone temperature, particularly at temperatures above 600°C. This behavior was consistent with the temperature dependence of the effusion cell’s cracking efficiency, as determined by residual gas analysis. The temporal stability of the arsenic source was excellent. Arsenic concentrations of 2.8×10²⁰ cm⁻³ were achieved at a cracker temperature of 800°C. The arsenic beam-equivalent pressure, estimated from an uncorrected, nude ion-gauge reading, was ∼8×10⁻⁷ mbar.     

In0.53Ga0.47As liquid phase epitaxy on (100)-InP substrates at low growth temperatures

In0.53Ga0.47As epitaxial layers of high quality and excellent surface morphology have been grown in an automated LPE system. The growth temperature was varied between 500 and 63O°C. Room-temperature Hall measurements indicated a net carrier concentration of n = 8 × 1014 cm?3 and mobility values of ? = 13000 cm2V?1 s?1 at TG 617°C and n = 7.7 × 1015 cm?3 and ? = 9800 cm2 V?1 s?1 at TG = 517°C, respectively.     

Antisite arsenic incorporation in the low temperature MBE of gallium arsenide: Physics and modeling

A stochastic model for simulating the surface growth processes in the low temperature molecular beam epitaxy of gallium arsenide is developed to investigate the incorporation of antisite As and its dependence on the growth conditions including the dynamics of the physisorbed As on the surface. Three different kinetic models with a combination of surface kinetic processes such as incorporation of antisite As, evaporation of antisite As and incorporation of regular As. The kinetic model with all three surface processes was accepted as the best model due to its physical soundness and reasonableness of its model parameters. The arsenic flux, temperature, and growth rate dependences of antisite arsenic (As_Ga) obtained from our simulation are in excellent agreement with the experimental results. The activation energy of 1.16 eV and a frequency factor of 4×10¹²/s for the evaporation of antisite arsenic obtained from our model are in good agreement with experimental and theoretical estimates. At a constant substrate temperature and growth rate, the antisite arsenic concentration increases with arsenic flux for low fluxes and saturates beyond a critical flux. The critical arsenic flux increases with temperature and the saturation value of the As_Ga concentration decreases with temperature. As the arsenic flux increases, the coverage of the physisorbed layer increases and at a critical flux dictated by the fixed temperature and growth rate, the coverage saturates at its maximum value of unity (a complete monolayer) and hence the concentration of As_Ga saturates. Lower As_Ga concentration results at higher temperature due to more evaporation of As_Ga. Additionally, an analytical model is developed to predict the As_Ga concentration for various growth conditions.     

Postgrowth heat-treatment effects in high-purity liquid-phase-epitaxial In0.53Ga0.47As

Heat treatment at 670°C for 20 min has been performed on high-purity In0.53Ga0.47As/InP: Fe layers grown by different melt-baking schemes. Layers with higher purity (?77 K ? 55000 cm2/Vs) exhibit increased resistivity and the presence of a deep level after the heat treatment. It is possible that the deep level, apparently 0.56 eV above the valence band, results from Fe outdiffusion from the substrate.     

Changes in annealing behaviour of SiO2 on Si resulting from H2+ and D2+ ion bombardment

Thermal oxides on 2?6 ?cm Si have been bombarded with 40 keV H2+ and 80 keV D2+ ions at almost grazing incidence (7.5°) to doses of 1015 ions cm?2. Anneals (30 and 45 min) were carried out in an r.f. furnace between 400 and 700°C in dry flowing N2 Implantation and subsequent annealing of bare oxide does not produce a Si/SiO2 structure which is superior to an Al/Si/SiO2 structure sintered at 400°C in dry N2. Implantation does however appear to suppress the development of large interface state densities at temperatures of 550°C and above, within the range investigated.     

Influence of arsenic incorporation on surface morphology and Si doping in GaAs(110) homoepitaxy

We have studied the relationship between the arsenic incorporation kinetics and the surface morphology and Si doping behaviour in GaAs(110) films grown by molecular beam epitaxy (MBE). The homoepitaxial growth of GaAs(110) requires low substrate temperatures and high As/Ga flux ratios to obtain films with good surface morphology, and under these conditions Si doped layers exhibit n-type behaviour. At higher growth temperatures and lower As/Ga flux ratios, the epitaxial films are highly faceted and the Si doped layers are p-type. We show that this growth related site switching behaviour and variation in surface morphology is due to a decrease in the As coverage arising from a small and temperature dependent incorporation coefficient of arsenic on this surface.     

Growth temperature dependence of low-noise MESFET in molecular-beam epitaxy

The substrate growth temperature dependence of electrical properties for a low-noise MESFET fabricated on MBE-grown material has been demonstrated. The optimum noise figure and its associated gain were attributed to the higher epilayer quality and mobility at a growth temperature of 650°C between temperatures of 550°C and 700°C.     

一种机载超宽带相控阵雷达T/R组件设计

为满足多功能电子系统对天线带宽、天线剖面和波束覆盖范围的需求,提出了一种工作在6~18 GHz的平面双极化低剖面宽角扫描相控阵天线. 首先,为了抑制由非平衡短路式巴伦引入的天线带内寄生谐振模式从而拓展天线带宽,在天线阵列中加入了由短路金属柱和印制金属盘构成的脊型结构;然后,设计了基于超表面的宽角扫描阻抗匹配层,以降低波束扫描时的反射损耗;此外,在该天线的介质层中设计了周期性分布的空气孔,以降低天线辐射体周围的有效介电常数,进而消除波束扫描时的表面波激励. 基于上述方法,利用多层印制电路板工艺,在保持天线低剖面特性的同时实现了超宽带宽角扫描性能. 仿真结果表明,该阵列在典型方位角φ=90°和φ=0°分别具备±75°和±60°的波束扫描能力,且阵列剖面高度小于3.52 mm. 为了验证该设计的正确性,制作了一个阵列规模为8×8的双极化天线样机并对其进行实验,实验结果与仿真结果吻合较好. 该天线具有超宽带、低剖面、宽角扫描特点,为多功能电子系统提供了一种新颖的天线阵结构.     

CdZnTe heteroepitaxy on 3″ (112) Si: Interface, surface, and layer characteristics

Tellurium adsorption studies were made on clean and arsenic passivated (112) silicon surfaces. Quantitative surface coverage values for tellurium were determined by Auger electron spectroscopy. Saturation coverage of up to 1.2 monolayers of tellurium could be obtained on a clean (112) silicon surface. On an arsenic passivated (112) Si surface however, the tellurium saturation coverage was limited to only ∼0.3 monolayer. Analysis of the adsorption behavior suggested that tellurium and arsenic chemisorption occurs preferentially at step edges and on terraces, respectively. The study revealed that arsenic passivation led to a significant decrease in the sticking coefficient of tellurium and an increase in it’s surface mobility. A model describing zinc telluride nucleation on a (112) Si surface is proposed. Thin templates of ZnTe followed by Cd_1−xZn_xTe layers were deposited on (112) Si by molecular beam epitaxy (MBE). The characteristics of the MBE Cd_1−xZn_xTe layers were found to be sensitive to the initial ZnTe nucleation and Si surface preparation.     

Use of tertiarybutylphosphine for the growth of InP and GaAs1-xPx

A newly-developed phosphorus source, tertiarybutylphosphine (TBP), which is much less toxic than PH₃, has been used to grow InP and GaAs_1-xP_x by atmospheric pressure organometallic vapor phase epitaxy (OMVPE). Excellent morphologies are obtained for the growth of InP between 560 and 630° C for TBP partial pressures larger than 0.5 x 10^-3. For the first time, V/III ratios as low as 3 have been used to grow InP epilayers with featureless morphologies at 600° C. To obtain good morphologies at both lower and higher temperatures, higher TBP partial pressures are necessary. The electron mobility increases and the electron density decreases as the temperature is increased. The highest room temperature mobilities and lowest electron densities, obtained at 630° C, are 3800 cm²/V-sec and 3 x 10¹⁵ cm^-3, respectively. The 10 K photoluminescence spectra of the InP epilayers at higher growth temperatures show no carbon contamination. Bound excition half widths as low as 3.0 meV have been measured. The use of TBP to replace PH₃ in the growth of GaAs_1-xP_x results in a nearly linear relationship between vapor and solid composition at 610° C,i.e., the P distribution coefficient is nearly unity. This contrasts sharply with the very low P distribution coefficient obtained using PH₃ at such low growth temperatures.     

真空电子束蒸发制备Nd∶YAG薄膜

采用真空电子束蒸发镀膜工艺制备纳米厚度的Nd∶YAG薄膜,经1 100 ℃真空高温退火处理使Nd∶YAG薄膜有效结晶,对Nd∶YAG薄膜的表面形貌、晶体结构、光致发光特性进行了测试.     

Pulsed thermal annealing of arsenic-implanted silicon

A pulsed thermal annealing system is described which rapidly heats samples to 700°C and can successfully activate and regrow arsenic-implanted damaged layers. The junctions so formed are shown to be of low resistivity and exhibit very good diode characteristics. Residual damage seen after the anneal does not appear to degrade the junction performance.     

High purity and chrome-doped GaAs buffer layers grown by liquid phase epitaxy for mesfet application

High purity GaAs buffer layers of carrier concentration in the low (l-5)×l0^l4/cm³ range with 77K electron mobility over 100,000 cm²/V-sec and 300K mobility around 8000 cm?/ V-sec have been grown by liquid phase epitaxy on Cr-doped GaAs substrates using the graphite sliding boat method. The high purity has been achieved with systematic and concurrent long term bake-outs (24 hrs) of both LPE melt and substrate, both exposed to the H₂ ambient gas stream at 775?C, prior to epitaxial growth at 700?C. Substrate surface degradation was reduced by using Ga:GaAs etch melts that were undersaturated at 700?C by 5? to 40?C. Best buffer layer morphologies with regard to surface planarity were obtained using etch melts that were saturated by near 85% of weight of GaAs at 700°C. The importance of substrate preconditioning in order to achieve the low ( 1 -2)×l0¹⁴ was examined and found to be critical. Melt and substrate bake outs at 800?C, and use of a 40?C undersaturated etch melt prior to epitaxial growth at 800?C resulted in a p-type layer of carrier concentration, 1 .9×l0^l2/cm³ and resistivity 1×10⁵ ohm-cm. Chromium doping at 700?C resulted in buffer layers with sheet resistivities greater than 10 ohms/sq and low pinhole densities.     

As Doping in (Hg,Cd)Te: An Alternative Point of View

Acceptor doping of many II–VI compound semiconductors has proved problematic and doping of epitaxial mercury cadmium telluride (MCT, Hg_1−x Cd _x Te) with arsenic is no exception. High-temperature (>400°C) anneals followed by a lower temperature mercury-rich vacancy-filling anneal are frequently required to activate the dopant. The model frequently used to explain p-type doping with arsenic invokes an amphoteric nature of group V atoms in the II–VI lattice. This requires that group VI substitution with arsenic only occurs under mercury-rich conditions either during growth or the subsequent annealing and involves site switching of the As. However, there are inconsistencies in the amphoteric model and unexplained experimental observations, including arsenic which is 100% active as grown by metalorganic vapor-phase epitaxy (MOVPE). A new model, based on hydrogen passivation of the arsenic, is therefore proposed.     

Tunable wettability of metallic films with assistance of porous anodic aluminum oxide

The present work demonstrates a simple method to prepare nanostructured Ni films with different morphologies with the assistance of porous anodic aluminum oxide (AAO) membranes. A great distinction is observed as the Ni films deposited onto the top and bottom sides of AAO membranes. The wetting properties of as-prepared membranes are investigated by measuring the contact angles of water on the surfaces. Results show that the static water contact angle changes dramatically from 124°±1° to 45°±1° on different Ni films, implying a change of the wettability from hydrophobicity to hydrophilicity affected by the surface patterns. This versatile approach can be conducted on various materials with potential applications in a broad range of fields.     

Effect of isovalent doping with phosphorus on the cluster formation in gallium arsenide grown by molecular-beam epitaxy at a relatively low temperature

Transmitting electron microscopy and X-ray diffractometry are used to study the GaAs layers undoped or doped uniformly with phosphorus (2.3 mol %) and grown at a temperature of 250°C and then annealed isochronously at 400, 500, 600, or 700°C. It is ascertained that doping with phosphorus reduces the amount of excess arsenic captured in the layer in the course of growth and also brings about a retardation of precipitation during subsequent annealing. The concentration of excess arsenic in undoped samples amounted to ～0.2 at %; clusters were observed after annealing at a temperature of 500°C. The concentration of excess arsenic amounted to 0.1 at % in the samples containing phosphorus; in this case, the clusters were observed only after a heat treatment at 600°C. The average size of clusters in doped samples is smaller than that in undoped samples at the same heat-treatment temperatures.     

Recent Advances in Gallium Phosphide Junction Devices for High-Temperature Electronic Applications

Recent advances in gallium phosphide technology are reviewed as they relate to high-temperature (T > 300°C) device applications. The electronic properties and materials aspects of GaP are summarized and compared to silicon and gallium arsenide. Minority-carrier unction devices are discussed as one area where this technology could have wide application. In this light, the high-temperature operation of two junction devices, a diode and a bipolar junction transistor (BJT), are displayed. The GaP diode is observed to provide excellent rectification properties with very low leakage over the full temperature range from 20°C to 400°C (< 3x10 -3A/cm2 at VR = 3 V, T = 400°C) and has demonstrated stable operation under bias for over 1000 h at 300°. The bipolar transistor has demonstrated constant current gain (6 < ? B < 10) and very low collector-base leakage for temperatures up to 450°C (ICO 80 μA at VCB = 3 V, T = 450°C). The contacting technology to GaP is identified as one area where additional work is necessary.     

Light sensitivity of Al0.25Ga0.75As/GaAs modulation-doped structures grown by molecular beam epitaxy: effect of substrate temperature

The sensitivity of carrier concentration and mobility of Al0.25Ga0.75As/GaAs modulation-doped structures to light exposure has been studied. The light sensitivity of both parameters was found to be strongly dependent on the growth temperature of the Al0.25Ga0.75As which was varied between 580°C and 695°C. A growth temperature of about 610°C was observed to produce the least light sensitivity, while a growth temperature of 660°C resulted in the most sensitivity to light. The corresponding minimum and maximum changes in carrier concentration, measured at 10 K, were 5% and 52% of the dark values, respectively, while changes in mobility were 2% and 40%, respectively. A persistent photoconductivity effect was also observed in the samples. The minimum in this effect was found to be a 1% change in 10 K carrier concentration at a growth temperature of 610°C.     

Chemical change from diffused hydrogen gas to hydroxyl ion in silica glass optical fibres

The chemical change from hydrogen gas that diffuses into silica glass for optical fibres to hydroxyl function has been investigated. Hydrogen molecules that diffuse into GeO2-doped silica glass at 500°C easily change into OH ions by thermal energy, while this chemical change does not occur in pure silica glass at 500°C. Also, germanium-doped silica fibre, in which hydrogen gas is dissolved at room temperature, shows OH ion absorption loss increase with chemical change by heat treatment at above 100°C, while pure silica core fibre shows no OH ion absorption loss increase by the same treatment.     

GaN-Based LEDs With AZO:Y Upper Contact

We report the fabrication of GaN-based light-emitting diodes (LEDs) with ytterbium-doped alumina-zinc-oxide (AZO:Y) upper contact. It was found that AZO and AZO:Y are both highly transparent in the visible region with good thermal stability optically. However, it was found that AZO:Y is much more thermally stable electrically, as compared with AZO. Furthermore, it was found that the output power of GaN LEDs with AZO upper contact decreased significantly from 2.80 to 2.30 mW after 700°C annealing. With the same annealing condition, it was found that output power decreased only slightly from 2.77 to 2.69 mW for the LEDs with AZO:Y upper contact.