Type I and Type II Alignment of the Light Hole Band in In0.15Ga0.85As/GaAs and in ln0.15Ga0.85As/Al0.15Ga0.85As Strained Quantum Wells

We present results of photoluminescence and cathodoluminescence measurements of strained undoped In_0.15Ga_0.85As/GaAs and In_0.15Ga_0.85As/Al_0.15Ga_0.85As quantum well structures, designed to throw light on the current controversy over light-hole band alignment at low In content. We compare these data with theoretical calculations of the confined state energies within the eight band effective mass approximation. Our analysis shows that for In_0.15Ga_0.85As/GaAs, the observed two transitions are consistent with either type I or type II alignment of the light hole band for band offset ratios within the accepted range. In the case of In_0.15Ga_0.85As/Al_0.15Ga_0.85As, however, our results clearly indicate type II alignment for the light hole band. We derive the band offset ratio Q, defined here as Q = δE_c/δE_g where δE_c is the conduction band offset and δE_g is the bandgap difference between the quantum well and the barrier in the presence of strain, for the In_0.15Ga_0.85As/Al_0.15Ga_0.85As system to be Q = 0.83 and discuss it in the context of the common anion rule.     

Electrical and growth characteristics of Au/Al0.15Ga0.85N:Si structures with various Si incorporations

We have investigated the growth characteristics of n-Al_0.15Ga_0.85N:Si/GaN and the electronic properties of Au/n-Al_0.15Ga_0.85N:Si diode structures grown by metal-organic chemical vapor deposition (MOCVD) with various Si incorporations. The Al_0.15Ga_0.85N:Si layers were grown on undoped GaN/sapphire (0001) epitaxial layers in a horizontal MOCVD reactor at the reduced pressure of 300 torr. The mirrorlike surface, free of defects, such as cracks or hillocks, can be seen in the undoped Al_0.15Ga_0.85N epilayer, which was grown without any intentional flow of SiH₄. However, many cracks are observed in the n-Al_0.15Ga_0.85N:Si, which was grown with Si incorporation above 1.0 nmol/min. While Au/n-Al_0.15Ga_0.85N:Si diodes having low incorporation of Si showed retively good rectifying behavior, the samples having high Si incorporation exhibited leaky current-voltage (I-V) behavior. Particularly, the Au/n-Al_0.15Ga_0.85N:Si structure grown with Si incorporation above 1.0 nmol/min cannot be used for electrical rectification. Both added tunneling components and thermionic emission influence the current transport at the Au/n-Al_0.15Ga_0.85N:Si barrier when Si incorporation becomes higher.     

Al0.85Ga0.15As/GaAs太阳能电池器件工艺优化研究

报道了优化的ｐ－ｎ型Ａｌ０．８５Ｇａ０．１５Ａｓ／ＧａＡｓ太阳能电池器件工艺。分别采用真空蒸发Ｃｒ／Ａｕ和ＡｕＧｅＮｉ／Ａｕ制作下面栅线和背面电极,并分别在４５０℃和３５０℃下快速合金化形成欧姆接触。采用ＮＨ４ＯＨ：Ｈ２Ｏ２：Ｈ３ＰＯ４：Ｈ２Ｏ体系的选择性腐蚀液去除高掺杂的ＧａＡｓ接触层。采用真空蒸发技术制备ＺｎＳ／ＭｇＦ２双层复合减反射层。测试结果表明,采用优化工艺制备的器件的光电转换效率得到了     

新型复合沟道Al0.3Ga0.7N/Al0.05Ga0.95N/GaN HEMT低相位噪声微波单片集成压控振荡器

设计并研制了一种新型复合沟道Al0.3Ga0.7N/Al0.05Ga0.95N/GaN HEMT(CC-HEMT)微波单片集成压控振荡器(VCO),且测试了电路的性能.CC-HEMT的栅长为1μm,栅宽为100μm.叉指金属-半导体-金属(MSM)变容二极管被设计用于调谐VCO频率.为提高螺旋电感的Q值,聚酰亚胺介质被插入在电感金属层与外延在蓝宝石上GaN层之间.当CC-HEMT的直流偏置为Vgs=-3V,Vds=6V,变容二极管的调谐电压从5.5V到8.5V时,VCO的频率变化从7.04GHz到7.29GHz,平均输出功率为10dBm,平均功率附加效率为10.4%.当加在变容二极管上电压为6.7V时,测得的相位噪声为-86.25dBc/Hz(在频偏100KHz时)和-108dB/Hz(在频偏1MHz时),这个结果也是整个调谐范围的平均值.据我们所知,这个相位噪声测试结果是文献报道中基于GaN HEMT单片VCO的最好结果.     

DC and RF characteristics of E-mode Ga/sub 0.51/In/sub 0.49/P-In/sub 0.15/Ga/sub 0.85/As pseudomorphic HEMTs

The DC and RF characteristics of Ga/sub 0.49/In/sub 0.51/P-In/sub 0.15/Ga/sub 0.85/As enhancement- mode pseudomorphic HEMTs (pHEMTs) are reported for the first time. The transistor has a gate length of 0.8 /spl mu/m and a gate width of 200 /spl mu/m. It is found that the device can be operated with gate voltage up to 1.6 V, which corresponds to a high drain-source current (I/sub DS/) of 340 mA/mm when the drain-source voltage (V/sub DS/) is 4.0 V. The measured maximum transconductance, current gain cut-off frequency, and maximum oscillation frequency are 255.2 mS/mm, 20.6 GHz, and 40 GHz, respectively. When this device is operated at 1.9 GHz under class-AB bias condition, a 14.7-dBm (148.6 mW/mm) saturated power with a power-added efficiency of 50% is achieved when the drain voltage is 3.5 V. The measured F/sub min/ is 0.74 dB under I/sub DS/=15 mA and V/sub DS/=2 V.     

p-GaN/Al0.35Ga0.65N/GaN应变量子阱肖特基紫外探测器

报道了p-GaN/Al0.35Ga0.65N/GaN应变量子阱结构的肖特基紫外探测器的制备及性能.器件的测试结果表明,在p-GaN/Al0.35Ga0.65N/GaN双异质结中强烈的压电极化和Stark效应共同作用下使得器件在正偏和反偏时的响应光谱都向短波方向移动了10nm.零偏下器件在280nm时的峰值响应为0.022A/W,在反向偏压为1V时,峰值响应增加到0.19A/W,接近理论值.在正向偏压下器件则呈平带状态,并在283和355nm处分别出现了两个小峰.在考虑极化的情况下,通过器件中载流子浓度分布的变化解释了器件在不同偏压下的响应特性,发现p-GaN/Al0.35Ga0.65N/GaN中的极化效应对器件的响应特性影响很大,通过改变偏压和适当的优化设计可以使探测器在紫外波段进行选择性吸收.     

p-GaN/Al0.35Ga0.65N/GaN应变量子阱肖特基紫外探测器

报道了p-GaN/Al0.35Ga0.65N/GaN应变量子阱结构的肖特基紫外探测器的制备及性能.器件的测试结果表明,在p-GaN/Al0.35Ga0.65N/GaN双异质结中强烈的压电极化和Stark效应共同作用下使得器件在正偏和反偏时的响应光谱都向短波方向移动了10nm.零偏下器件在280nm时的峰值响应为0.022A/W,在反向偏压为1V时,峰值响应增加到0.19A/W,接近理论值.在正向偏压下器件则呈平带状态,并在283和355nm处分别出现了两个小峰.在考虑极化的情况下,通过器件中载流子浓度分布的变化解释了器件在不同偏压下的响应特性,发现p-GaN/Al0.35Ga0.65N/GaN中的极化效应对器件的响应特性影响很大,通过改变偏压和适当的优化设计可以使探测器在紫外波段进行选择性吸收.     

n-Al0.15Ga0.85 N/p-6H–SiC heterostructure and based bipolar transistor

Heterojunction bipolar transistor (HBTs) based on Al0.15Ga0.85 N/6H–SiC heterojunction was fabricated. Room-temperature current–voltage (I–V) characteristics of n-Al0.15Ga0.85 N/p-6H–SiC emitter–base heterojunction exhibited good rectifying behavior with a forward current 5 × 10⁻² A and reverse current 3 × 10⁻⁹ A at 10 V and −10 V, respectively. Analysis of the temperature dependent I–V characteristics of this heterojunction revealed a barrier height of 1.1 eV. The fabricated n-Al0.15Ga0.85 N/p-SiC/n-SiC bipolar transistor did not exhibit common-emitter operation, however, common-base operation was observed with current gain β = IC/IB ranging in 75–100.     

Investigation of the impact of Al mole-fraction on the consequences of RF stress on Al/sub x/Ga/sub 1-x/N/GaN MODFETs

Variations of the low-frequency noise (LFN), power, and dc characteristics of a variety of SiN/sub x/ passivated AlGaN/GaN MODFETs with different values of Al mole-fraction, gate length, and gate drain spacing upon RF stress are investigated. It is experimentally evidenced that the variation of Al mole-fraction (x) of the barrier Al/sub x/Ga/sub 1-x/N layer from 0.2 to 0.4, has no considerable impact on the drain and gate low-frequency noise current characteristics. The most noticeable variation on the device characteristics upon long-term RF stressing has been on the pinch-off voltage. Although no material degradation by increasing the Al mole-fraction has been evidenced through the low-frequency noise data, it is observed that the variation of pinch-off voltage upon RF stressing becomes more important as the Al mole-fraction increases.     

Optical properties of strained layer (111)B Al0.15Ga0.85As-In0.04Ga0.96as quantum well heterostructures

Data presented here demonstrate that strained-layer (111)B Al_0.15Ga_0.85As-In_0.04Ga_0.96As quantum wells exhibit unique optical properties when compared to otherwise identical (100) oriented strained layers. Photoluminescence measurements identify a strain-induced electric field of order 6.7 Vμm^-1 within the (111)B quantum well that is not present for the (100) case. Photoluminescence excitation spectroscopy measurements show that the heavy-hole to light-hole energy band splitting is approximately 7 meV larger for the (111)B structure than for the (100) structure. Howard Hughes Doctoral Fellow IBM Graduate Fellow     

Electrical and Optical Characterization of Ni/Al0.3Ga0.7N/GaN Schottky Barrier Diodes

Ni/AlGaN/GaN Schottky barrier diodes were characterized by electrical and optical measurements. Analysis of temperature-dependent (80?K to 550?K) current–voltage characteristics considering various transport mechanisms shows that the tunneling current dominates in the samples investigated. Thermionic emission current, extracted from the total current by a fitting procedure, yielded an effective barrier height of 1.36?eV to 1.39?eV at 300?K, and its slight decrease with increased temperature. This result shows that significantly lower barrier heights reported before (0.73?eV to 0.96?eV) follow from an assumption that the measured and thermionic currents are equal. The barrier height of 1.66?eV extracted from photoemission measurements confirms that electrically evaluated barrier heights are underestimated. The tunneling current contribution is considered to be dislocation governed, and a dislocation density of about 2?×?10⁸?cm^?2 is calculated.     

Broadband microwave noise characteristics of high-linearity composite-channel Al/sub 0.3/Ga/sub 0.7/N/Al/sub 0.05/Ga/sub 0.95/N/GaN HEMTs

We report broadband microwave noise characteristics of a high-linearity composite-channel HEMT (CC-HEMT). Owing to the novel composite-channel design, the CC-HEMT exhibits high gain and high linearity such as an output third-order intercept point (OIP3) of 33.2 dBm at 2 GHz. The CC-HEMT also exhibits excellent microwave noise performance. For 1-/spl mu/m gate-length devices, a minimum noise figure (NF/sub min/) of 0.7 dB and an associated gain (G/sub a/) of 19 dB were observed at 1 GHz, and an (NF/sub mi/) of 3.3 dB and a G/sub a/ of 10.8 dB were observed at 10 GHz. The dependence of the noise characteristics on the physical design parameters, such as the gate-source and gate-drain spacing, is also presented.     

High uniformity of Al0.3Ga0.7As/ln0.15Ga0.85As doped-channel structures grown by molecular beam epitaxy on 3″ GaAs substrates

Al_0.3Ga_0.7As/ln_0.15Ga_0.85As doped-channel structures were grown by molecular beam epitaxy on 3″ GaAs substrates. The uniformities of electrical and optical properties across a 3″ wafer were evaluated. A maximum 10% variation of sheet charge density and Hall mobility was achieved for this doped-channel structure. A1 μm long gate field-effect transistor (FET) built on this layer demonstrated a peak transconductance of 350 mS/mm with a current density of 470 mA/mm. Compared to the high electron mobility transistors, this doped-channel FET provides a higher current density and higher breakdown voltage, which is very suitable for high-power microwave device applications.     

Low-operation voltage of InGaN/GaN light-emitting diodes by using aMg-doped Al0.15Ga0.85N/GaN superlattice

Low-resistivity Mg-doped Al_0.15Ga_0.85N/GaN strained-layer superlattices were grown. In these superlattices, the maximum hole concentration is 3×10¹⁸/cm³ at room temperature. Hall-effect measurements indicate high conductivity of this structure in which the high activation efficiency is attributed to the strain-induced piezoelectric fields. This work also fabricated InGaN/GaN blue LEDs that consist of a Mg-doped Al_0.15Ga_0.85N/GaN SLs. Experimental results indicate that the LEDs can achieve a lower operation voltage of around 3 V, i.e., smaller than conventional devices which have an operation voltage of about 3.8 V     

Comparing GaAs and In0.15Ga0.85As as channel material for alternative substrate CMOS

Photoluminescence intensity (PLI) measurements of GaAs and InGaAs thin films indicate that InGaAs might be inherently easier to passivate than GaAs. The introduction of just 15% of In leads to a reduction of the surface recombination velocity at native oxide interfaces by an order of magnitude. This is more than the effect expected by a reduced bandgap alone. The PLI method applied to thin films can also be used to determine the surface recombination velocity of other IIIV-oxide interfaces.     

Submicron-gate ion-implanted In/sub 0.15/Ga/sub 0.85/As/GaAs MESFETs with graded indium composition

0.25 mu m and 0.5 mu m gate ion-implanted MESFETs have been fabricated on In/sub 0.15/Ga/sub 0.85/As epitaxial layers. These layers are grown by MOCVD on three inch diameter GaAs substrates with the indium mole fraction graded from 15% at the InGaAs/GaAs heterointerface to 0% at the surface. Both devices show excellent DC and microwave performance. From S-parameter measurements, extrinsic current gain cutoff frequencies f/sub t/ of 120 and 61 GHz are obtained for the 0.25 mu m and 0.5 mu m gate MESFETs, respectively. The authors investigate the potential of small-bandgap InGaAs materials for submicron-gate MESFET applications.<>     

Effect of Annealing on the Characteristics of Pd/Au Contactsto p-Type GaN/Al0.45Ga0.55N

The effect of annealing on the characteristics of Pd/Au contacts to p-type GaN/Al_0.45Ga_0.55N was investigated. The electrical characteristics of Pd/Au contacts and a p-GaN/AlGaN sample were measured after annealing at different temperatures from 550°C to 850°C. Changes in the surface electrical characteristic of p-GaN/AlGaN material were observed after each annealing step. It is indicated that the surface electrical characteristic of p-GaN/AlGaN material plays an important role in the current transport through Pd/Au pads. A possible reason for those changes is impurity contamination, most likely oxygen and carbon contamination introduced from processing. The microstructure of Pd on p-GaN/AlGaN was investigated by glancing-incidence x-ray diffraction (GXRD). The results of GXRD show that the AlPd₂ and GaPd₂ phases were formed at the interface after annealing, and the formation of these phases could be effective for forming ohmic contacts on p-GaN/AlGaN.     

Flicker noise in GaN/Al0.15Ga0.85N dopedchannel heterostructure field effect transistors

We have investigated noise characteristics of novel GaN/Al_0.15Ga_0.85N doped channel heterostructure field effect transistors designed for high-power density applications. The measurements were carried out for various gate bias voltages V_GS and with the drain voltage V_DS varying from the linear to the saturation regions of operation V_DS>5 V. Our results show that flicker, e.g., 1/f noise, is the dominant limiting noise of these devices; and the Hooge parameter is of the order of 10 ^-5-10^-4. The gate voltage dependence of 1/f noise was observed in the linear region for all examined V_GS and in the saturation region for V_GS>0. These results indicating low values of the Hooge parameter are important for microwave applications     

背入射Al0.42 Ga0.58 N/Al0.40 Ga0.60 N异质结p-i-n太阳光盲紫外探测器

在蓝宝石上用MOCVD生长的材料制备了背入射Al0.42Ga0.58N/Al0.40Ga0.60N异质结p-I-n太阳光盲紫外探测器.从器件的正向Ⅰ-Ⅴ特性曲线计算了理想因子n与串联电阻Rs分别为3和93?器件在零偏压下275nm峰值波长处的外量子效率与探测率分别为9%和4.98×1011cm·Hz1/2/W,分析表明Al0.42Ga0.58N窗口层在275nm波长处的透过率仅为15.7%,是器件外量子效率和探测率偏低的原因之一.     

背入射Al0.42Ga0.58N/Al0.40Ga0.60N 异质结 p-i-n 太阳光盲紫外探测器成

在蓝宝石上用MOCVD生长的材料制备了背入射Al0.42Ga0.58N/Al0.40Ga0.60N 异质结 p-i-n 太阳光盲紫外探测器. 从器件的正向I-V特性曲线计算了理想因子n与串联电阻RS分别为3和93Ω. 器件在零偏压下275nm峰值波长处的外量子效率与探测率分别为9%和4.98e11cm·Hz1/2/W,分析表明Al0.42Ga0.58N窗口层在275nm波长处的透过率仅为15.7%,是器件外量子效率和探测率偏低的原因之一.