Improved surface and electrical properties of passivated GaSb with less alkaline sulfide solution

The surface quality of HCl-etched and ammonium sulfide [(NH₄)₂S]-based treated bulk n-GaSb(100) were compared using x-ray photoelectron spectroscopy (XPS) and TOF-SIMS. It has been found that native oxides present on the GaSb surface are more effectively removed when etched with concentrated HCl solution. With additional [(NH₄)₂SO₄+S] substances or hydrogen ions in the passivation solution, the treated samples displayed significant reduction of native oxides and formation of the sulfides compared with pure (NH₄)₂S solution. The treated samples also result in a noteworthy improvement in the current–voltage (I–V) characteristics of Au/n-GaSb Schottky contacts, as evidenced by the lower ideality factor (n), higher barrier height (Φ_b) and higher rectification ratio at ±0.2 V. The I–V measurement provided definitive confirmation of XPS and TOF-SIMS results, establishing the need for less alkaline solution for greater passivation stability.     

Electrical and optical property of annealed Te-doped GaSb

GaSb is the most suitable substrate in the epitaxial growth of mixed semiconductors of GaSb system. In this work, Te-doped GaSb bulk crystals with different doping concentration have been annealed at 550 ℃ for 100 h in ambient antimony. The annealed samples have been studied by Hall effect measurement, infrared (IR) optical transmission, Glow discharge mass spectroscopy (GDMS) and photoluminescence (PL) spectroscopy. After annealing, Te-doped GaSb samples exhibit a decrease of carrier concentration and increase of mobility, along with an improvement of below gap IR transmission. Native acceptor related electrical compensation analysis suggests a formation of donor defect with deeper energy level. The mechanism of the variation of the defect and its influence on the material properties are discussed.     

SiC肖特基势垒二极管的反向特性

在n型4H-SiC衬底上的n型同质外延层的Si面制备了纵向肖特基势垒二极管(SBD),研究了场板、场限环及其复合结构等不同终端截止结构对于反向阻断电压与反向泄漏电流的影响。场板(FP)结构有利于提高反向阻断电压,减小反向泄漏电流。当场板长度从5μm变化到25μm,反向阻断电压随着场板长度的增加而增加。SiO2厚度对于反向阻断电压有重要的影响,当厚度为0.5μm,即大约为外延层厚度的1/20时,可以得到较大的反向阻断电压。当场限环的离子注入区域宽度从10μm变化到70μm,反向阻断电压也随之增加。FLR和FP复合结构对于改善反向阻断电压以及反向泄漏电流都有作用,同时反向阻断电压对于场板长度不再敏感。采用复合结构,在10μA反向泄漏电流下最高阻断电压达到1 300V。讨论了离子注入剂量对于反向阻断电压的影响,注入离子剂量和反向电压的关系表明SBD结构不同于传统PIN结构的要求。当采用大约为150%理想剂量的注入剂量时才可达到最高的反向阻断电压而不是其他报道的75%理想剂量,此时的注入剂量远高于PIN结构器件所需的注入剂量。     

Material and electrical characteristics of iron doped Pt-lnAIAs schottky diodes grown by LP-MOCVD

InAlAs lattice-matched to InP is of great importance as a large bandgap material for various InP-based heterostructures device applications. However, growth of good quality InAlAs using metalorganic chemical vapor deposition (MOCVD) is relatively difficult due to the reactive nature of its aluminum sources. In this paper, we present the use of iron as a possible dopant to improve the electrical properties of MOCVD grown InAlAs. Time resolved photoreflectance was used to confirm the increase in trap levels with increased iron doping. The impact of iron doping on the electrical properties of devices was investigated using Pt-Schottky diodes fabricated on undoped and iron doped InAlAs materials. Low frequency noise measurements were also carried out to investigate the impact of iron incorporation on the noise characteristics of the devices. Although noise levels showed marginal difference between undoped and iron doped materials, iron doped InAlAs showed a Lorentzian component in the noise spectra which is not found in undoped materials. An activation energy of ∼0.77 eV was evaluated for traps introduced by iron incorporation using temperature dependent low frequency noise measurements.     

The effect of substrate misorientation on the optical, structural, and electrical properties of GaN grown on sapphire by MOCVD

We report the growth and characterization of unintentionally doped GaN on both exact and vicinal (0001) sapphire substrates. The GaN heteroepitaxial layers are grown by metalorganic chemical vapor deposition on c-plane A1₂O₃ substrates either on-axis or intentionally misoriented 2° toward the a-plane (1120) or 5 or 9° toward the m-plane (10 10). The samples are characterized by 300K photoluminescence, cathodoluminescence, and Hall-effect measurements as well as by triple-axis x-ray diffractometry to determine the effect of the misorientation on the optical, electrical, and structural properties of heteroepitaxial undoped GaN. Ten different sample sets are studied. The data reveal enhanced photo-luminescence properties, increased electron mobility, a reduced n-type background carrier concentration, and a somewhat degraded surface morphology and crystalline quality for the misoriented samples compared to the on-axis samples.     

Structural, electrical and magnetic characterizations of Ni/Cu/p-Si Schottky diodes prepared by liquid phase epitaxy

In this paper, we have investigated the structural, electrical and magnetic characterizations of Ni/Cu/p-Si Schottky diode prepared by liquid phase epitaxy (LPE). Current density-voltage (J-V), capacitance-voltage (C-V) and capacitance-frequency (C-f) measurements were performed to determine the conduction mechanisms as well as extracting the important diode parameters. Rectifying properties were obtained, which definitely of the Schottky diode type. At low voltages, (0 < V ? 0.4 V), current density in the forward direction was found to obey the diode equation, while for higher voltages, (0.5 < V ? 1.5 V), conduction was dominated by a space-charge-limited conduction (SCLC) mechanism. Analysis of the experimental data under reverse bias suggests a transition from electrode-limited to a bulk-limited conduction process for lower and higher applied voltages, respectively. Diode parameters such as, the built-in potential, V_b, the carrier concentration, N, the width of the depletion layer, W, of the Ni/Cu/p-Si Schottky diode were obtained from the C-V measurements at high frequency (1 MHz). The capacitance-frequency measurements showed that the values of capacitance were highly frequency dependent at low frequency region but independent at high frequencies. The Ni/Cu/p-Si Schottky diode showed magnetic properties due to the effect of Ni in the heterostructure.     

Control of Electrophosphorescence in Conjugated Dendrimer Light‐Emitting Diodes

We present a novel platinum porphyrin based phosphorescent dendrimer for use as a triplet harvesting dopant in organic light‐emitting diodes. Two types of dendritic host materials are used. Through the choice of a common branching architecture around the emissive chromophore unit of both guest and host materials, we are able to achieve excellent miscibility. The relative contribution of guest to host emission is found to depend strongly on the energy level offsets of the two blend materials, indicating strong trapping processes. Under pulsed operation, we observe a striking dependence of the emission spectrum on pulse period, independent of the host material used. This spectral modification is attributed to the quenching of triplet excitations at high excitation densities. We find excellent agreement between our measured data and a model based on bimolecular recombination.     

InSb,GaSb, and GaInSb grown using trisdimethylaminoantimony

GalnSb alloys as well as the constituent binaries InSb and GaSb have been grown by organometallic vapor phase epitaxy using the new antimony precursor trisdimethylaminoantimony (TDMASb) combined with conventional group III precursors trimethylindium (TMIn) and trimethylgallium (TMGa). InSb layers were grown at temperatures between 275 and 425°C. The low values of V/III ratio required to obtain good morphologies at the lowest temperatures indicate that the pyrolysis temperature is low for TDMASb. In fact, at the lowest temperatures, the InSb growth efficiency is higher than for other antimony precursors, indicating the TDMASb pyrolysis products assist with TMIn pyrolysis. A similar, but less pronounced trend is observed for GaSb growth at temperatures of less than 500°C. No excess carbon contamination is observed for either the InSb or GaSb layers. Ga_1-xIn_xSb layers with excellent morphologies with values of x between 0 and 0.5 were grown on GaSb substrates without the use of graded layers. The growth temperature was 525°C and the values of V/III ratio, optimized for each value of x, ranged between 1.25 and 1.38. Strong photoluminescence (PL) was observed for values of x of less than 0.3, with values of halfwidth ranging from 13 to 16 meV, somewhat smaller than previous reports for layers grown using conventional precursors without the use of graded layers at the interface. The PL intensity was observed to decrease significantly for higher values of x. The PL peak energies were found to track the band gap energy; thus, the luminescence is due to band edge processes. The layers were all p-type with carrier concentrations of approximately 10¹⁷ cm³. Transmission electron diffraction studies indicate that the Ga_0.5In_0.5 Sb layers are ordered. Two variants of the Cu-Pt structure are observed with nearly the same diffracted intensities. This is the first report of ordering in GalnSb alloys.     

Analysis of structural, optical and electrical properties of metal/p-ZnO-based Schottky diode

A systematic study of the behaviour of Pd/p-ZnO thin film Schottky diode has been reported. The p-type ZnO thin film with improved stability has been grown on n-type Si by doping ZnO with copper.μSeebeck measurement confirmed the p-type nature of Cu-doped ZnO thin film. The X-ray diffraction spectra of the deposited film revealed polycrystalline nature with preferred growth orientation of (101) of ZnO film. The surface morphological study demonstrated the conformal deposition of a thin film over n-Si wafer. The estimated bandgap of Cu-doped p-type ZnO thin film from ellipsometric measurement turns out to be 3.14 eV at 300 K. The measured electrical parameters of the proposed Pd/p-ZnO Schottky diode have also been validated by the results of numerical simulation obtained by using ATLAS^TM device simulator.     

Effect of ion damage on the electrical and optical behavior of p-type GaAs and InGap

The effect of ion damage generated by exposure to argon or hydrogen electron cyclotron resonance plasmas at various conditions was investigated for p-InGaP and p-GaAs. Room temperature photoluminescence (PL) and either capacitance-voltage or Hall measurements were performed to determine the effect of these various treatments on the efficiency of band edge recombination and the electrical compensation. The feasibility of damage removal was investigated by examining the electrical and optical behavior after annealing at various temperatures. For argon plasma exposed InGaP, restoration of the PL intensity to ∼30% of as-grown sample could be achieved at modest annealing temperatures of ∼600°C. For hydrogen plasma exposed carbon doped GaAs, on the other hand, almost 80 ∼ 90% of the PL intensity of the as-grown sample could be recovered at 600°C. For heavily C-doped GaAs (p ∼ 10²¹cm⁻³), there was significant degradation of the optical properties at annealing temperatures ≥600°C.     

Using Self‐Assembling Dipole Molecules to Improve Hole Injection in Conjugated Polymers

Surface modification of indium‐tin‐oxide (ITO)‐coated substrates through the use of self‐assembled monolayers (SAMs) of molecules with permanent dipole moments has been used to control the ITO work function and device performance in polymer light‐emitting diodes based on a polyfluorene hole transporting copolymer. Measured current–voltage characteristics of the devices reveal greatly increased hole injection currents from the SAM‐altered electrodes with higher work function, in agreement with an expected reduction in the barrier for hole injection. In particular, it is shown that the SAM‐modified electrode with the highest work function provides an ohmic contact for hole injection into the studied polymer. Injection from the widely used poly(2,3‐ethylenedioxythiophene)/polystyrenesulphonic acid (PEDOT:PSS)‐coated ITO anode system, is less efficient compared with some of the studied SAM‐coated ITO anodes despite the significantly higher work function measured by a Kelvin probe. This apparently anomalous situation is attributed to the inhomogenities in the injection processes that occur over the area of the device when the PEDOT:PSS‐coated ITO electrode is used.     

The source of negative capacitance and anomalous peak in the forward bias capacitance-voltage in Cr/p-si Schottky barrier diodes (SBDs)

The frequency and voltage dependence of capacitance–voltage (C–V) and conductance-voltage (G/ω−V) characteristics of the Cr/p-Si metal semiconductor (MS) Schottky barrier diodes (SBDs) were investigated in the frequency and applied bias voltage ranges of 10 kHz to 5 MHz and (−4 V)−(+4 V), respectively, at room temperature. The effects of series resistance (R_s) and density distribution of interface states (N_ss), both on C–V and G/ω−V characteristics were examined in detail. It was found that capacitance and conductance, both, are strong functions of frequency and applied bias voltage. In addition, both a strong negative capacitance (NC) and an anomalous peak behavior were observed in the forward bias C–V plots for each frequency. Contrary to the behavior of capacitance, conductance increased with the increasing applied bias voltage and there happened a rapid increase in conductance in the accumulation region for each frequency. The extra-large NC in SBD is a result of the existence of R_s, N_ss and interfacial layer (native or deposited). In addition, to explain the NC behavior in the forward bias region, we drew the C–I and G/ω−I plots for various frequencies at the same bias voltage. The values of C decrease with increasing frequency at forward bias voltages and this decrease in the NC corresponds to an increase in conductance. The values of N_ss were obtained using a Hill–Coleman method for each frequency and it exhibited a peak behavior at about 30 kHz. The voltage dependent profile of R_s was also obtained using a Nicollian and Brews methods.     

Electrical and optical activation studies of Si-implanted GaN

Comprehensive and systematic electrical and optical activation studies of Si-implanted GaN were made as a function of ion dose and anneal temperature. Silicon ions were implanted at 200 keV with doses ranging from 1×10¹³ cm^?2 to 5×10¹⁵ cm^?2 at room temperature. The samples were proximity-cap annealed from 1050°C to 1350°C with a 500-Å-thick AlN cap in a nitrogen environment. The optimum anneal temperature for high dose implanted samples is approximately 1350°C, exhibiting nearly 100% electrical activation efficiency. For low dose (≤5×10¹⁴ cm^?2) samples, the electrical activation efficiencies continue to increase with an anneal temperature through 1350°C. Consistent with the electrical results, the photoluminescence (PL) measurements show excellent implantation damage recovery after annealing the samples at 1350°C for 20 sec, exhibiting a sharp neutral-donor-bound exciton peak along with a sharp donor-acceptor pair peak. The mobilities increase with anneal temperature, and the highest mobility obtained is 250 cm²/Vs. The results also indicate that the AlN cap protected the implanted GaN layer during high-temperature annealing without creating significant anneal-induced damage.     

Effect of a thin W, Pt, Mo, and Zr interlayer on the thermal stability and electrical characteristics of NiSi

It is reported that the thermal stability of NiSi is improved by employing respectively the addition of a thin interlayer metal (W, Pt, Mo, Zr) within the nickel film. The results show that after rapid thermal annealing (RTA) at temperatures ranging from 650 °C to 800 °C, the sheet resistance of formed ternary silicide Ni(M)Si was less than 3 Ω/□, and its value is also lower than that of pure nickel monosilicide. X-ray diffraction (XRD) and raman spectra results both reveal that only the Ni(M)Si phase exists in these samples, but the high resistance NiSi₂ phase does not. Fabricated Ni(M)Si/Si Schottky barrier devices displayed good I-V electrical characteristics, with the barrier height being located generally between 0.65 eV and 0.71 eV, and the reverse breakdown voltage exceeding to 40 V. It shows that four kinds of Ni(M)Si film can be considered as the satisfactory local connection and contact material.     

Effect of high-temperature processing on the creation of boron-related deep levels in 4H-SiC

High-temperature processing was applied to SiC boron-doped epitaxial layers, epitaxial layers grown on boron-rich substrates, and boron-implanted samples in order to establish conditions favorable for the formation of boron-related centers (D-centers) that introduce a deep level in SiC bandgap. Photoluminescence (PL) was used to detect and compare the formation of the D-center after different processing steps. It was confirmed that the presence of lattice defects was required for achieving significant boron diffusion and D-center formation. In addition, epitaxial growth on the top of a boron-implanted sample yielded efficient boron in-diffusion in the growing layer, which resulted in a material compensated with D-centers. The temperature dependence of the D-center formation efficiency was investigated.     

采用光激励和光检测的LED电特性测试方法

针对目前用于测试LED光电特性多采用接触式的电注入检测方法存在系统复杂、成本高、检测效率低且易造成芯片损伤等不足,提出一种采用光激励和光检测的非接触式检测方法。通过获取光激励LED p-n结产生的光致发光（PL）光谱,在建立了LED PL、电致发光（EL）效应间的确切联系以及LED发光光谱特性与其电特性间的对应关系的基...     

Electrical and optical properties of oxygen doped GaN grown by MOCVD using N2O

Oxygen doped GaN has been grown by metalorganic chemical vapor deposition using N₂O as oxygen dopant source. The layers were deposited on 2″ sapphire substrates from trimethylgallium and especially dried ammonia using nitrogen (N₂) as carrier gas. Prior to the growth of the films, an AIN nucleation layer with a thickness of about 300? was grown using trimethylaluminum. The films were deposited at 1085°C at a growth rate of 1.0 μm/h and showed a specular, mirrorlike surface. Not intentionally doped layers have high resistivity (>20 kW/square). The gas phase concentration of the N₂O was varied between 25 and 400 ppm with respect to the total gas volume. The doped layers were n-type with carrier concentrations in the range of 4×10¹⁶ cm⁻³ to 4×10¹⁸ cm⁻³ as measured by Hall effect. The observed carrier concentration increased with increasing N₂O concentration. Low temperature photoluminescence experiments performed on the doped layers revealed besides free A and B exciton emission an exciton bound to a shallow donor. With increasing N₂O concentration in the gas phase, the intensity of the donor bound exciton increased relative to that of the free excitons. These observations indicate that oxygen behaves as a shallow donor in GaN. This interpretation is supported by covalent radius and electronegativity arguments.     

Electrical and optical characterization studies of lower dose Si-implanted AlxGa1−xN

Electrical and optical activation studies of lower dose Si-implanted Al_xGa_1?xN (x=0.14 and 0.24) have been made systematically as a function of ion dose and anneal temperature. Silicon ions were implanted at 200 keV with doses ranging from 1×10¹³ cm^?2 to 1×10¹⁴ cm^?2 at room temperature. The samples were proximity cap annealed from 1,100°C to 1,350°C with a 500-Å-thick AlN cap in a nitrogen environment. Nearly 100% electrical activation efficiency was obtained for Al_0.24Ga_0.76N implanted with a dose of 1 × 10¹⁴ cm^?2 after annealing at an optimum temperature around 1,300°C, whereas for lower dose (≤5×10¹³ cm^?2) implanted Al_0.24Ga_0.76N samples, the electrical activation efficiencies continue to increase with anneal temperature up through 1,350°C. Seventy-six percent electrical activation efficiency was obtained for Al_0.14Ga_0.86N implanted with a dose of 1 × 10¹⁴ cm^?2 at an optimum anneal temperature of around 1,250°C. The highest mobilities obtained were 89 cm²/Vs and 76 cm²/Vs for the Al_0.14Ga_0.86N and Al_0.24Ga_0.76N, respectively. Consistent with the electrical results, the photoluminescence (PL) intensity of the donor-bound exciton peak increases as the anneal temperature increases from 1,100°C to 1,250°C, indicating an increased implantation damage recovery with anneal temperature.     

Experimental and numerical analysis of channel-length-dependent electrical properties in bottom-gate,bottom-contact organic thin-film transistors with Schottky contact

Channel length dependence of field-effect mobility and source/drain parasitic resistance in pentacene thin-film transistors with a bottom-gate, bottom-contact configuration was investigated. Schottky barrier effect such as nonlinear behaviors in transistor output characteristics appeared and became more prominent for shorter channel length less than 10 μm, raising some concerns for a simple utilization of conventional parameter extraction methods. Therefore the gate-voltage-dependent hole mobility and the source/drain parasitic resistance in the pentacene transistors were evaluated with the aid of device simulation accounting for Schottky contact with a thermionic field emission model. The hole mobility in the channel region shows smaller values with shorter channel length even after removing the influence of Schottky barrier, suggesting that some disordered semiconductor layers with low carrier mobility exist near the contact electrode. This experimental data analysis with the simulation enables us to discuss and understand in detail the operation mechanism of bottom-gate, bottom-contact transistors by considering properly each process of charge carrier injection, carrier flow near the contact region, and actual channel transport.     

Photoluminescence and Electroluminescence Imaging of Carrot Defect in 4H-SiC Epitaxy

Electroluminescence (EL) and photoluminescence (PL) imaging techniques were successfully used to reveal defect features in 34 carrots in 4H-SiC epilayers. Because EL and PL techniques are nondestructive and require minimal sample preparations, many carrots can be examined over a reasonable time. Our findings showed that some carrots had the basic components consistent with the model proposed by Benamara et al., but also contained additional features beyond the basic components. Eight carrots contained multiple bright line features, and 25 out of 50 bright line features exhibited multiple line characteristics. Eleven carrots were discovered to contain basal plane faults (B’s) and the corresponding small stacking faults (S’s) near the carrot heads. Not all the carrots lie along the off-cut direction; a couple were oriented 5° from the off-cut. Of the seven carrots with shape lengths -200 μm, one had a corresponding bright line length of 370 μm. Based on this line length, the calculated depth of origin was about midway in the epilayer, while all of the other carrots originated from the substrate. In summary, both EL and PL techniques were consistent in showing that carrots exhibit variable defect structures on a microscopic scale.