Dramatic reduction in dark current of β-Ga2O3 ultraviolet photodectors via β-(Al0.25Ga0.75)2O3 surface passivation

Solar-blind ultraviolet photodetectors with metal-semiconductor-metal structure were fabricated based on β -(Al_0.25Ga_0.75)₂O₃/β -Ga₂O₃ film grown by metal-organic chemical vapor deposition. It was known that various surface states increase dark current and a large number of defects can hinder the transport of carriers, resulting in low switching ratio and low responsivity of the device. In this work, β -(Al_0.25Ga_0.75)₂O₃ films are used as surface passivation materials. Owning to its wide band gap, we obtain excellent light transmission and high lattice matching with β -Ga₂O₃. We explore the change and mechanism of the detection performance of the β -Ga₂O₃ detector after β -(Al_0.25Ga_0.75)₂O₃ surface passivation. It is found that under the illumination with 254 nm light at bias 5 V, the β -(Al_0.25Ga_0.75)₂O₃/β -Ga₂O₃ photodetectors show dark current of just 18 pA and high current on/off ratio of 2.16×10⁵. The dark current is sharply reduced about 50 times after passivation of the β -Ga₂O₃ surface, and current on/off ratio increases by approximately 2 times. It is obvious that β -Ga₂O₃ detectors with β -(Al_0.25Ga_0.75)₂O₃ surface passivation can offer superior detector performance.     

Effects of pH and citric acid contents on characteristics of ester-derived BaFe12O19 powder

The single domain size of BaFe₁₂O₁₉ powder with crystallite sizes less than 200 nm was produced using a citric acid precursor method. Fe³⁺ and Ba²⁺, in a molar ratio of 12, were chelated by COOH⁻ in an aqueous solution. After ethylene glycol additions, esterification, dehydration, and calcination led to the formation of ester-derived BaFe₁₂O₁₉ powder. High pH and/or high citric acid contents in the starting solution are required to complete chelate metallic ions in the solution and to form pure barium ferrite powder at 1073 K. Pure single magnetic domain BaFe₁₂O₁₉ particles of M(30 kOe)≈54 emu/g, M_r≈28 emu/g, and H_c≈3.7 kOe were produced using [citric acid]/[metallic ions]=1.5 and pH7.     

Dry-etching processes for high-temperature superconductors

Patterning of thin films and multilevel structures of high-temperature superconductors is a key technology for microelectronic applications. We performed a comparative study of Ion Beam Etching (IBE) and Reactive Ion Etching (RIE) processes for YBa₂Cu₃O_7−δ thin films. The RIE process with a pure chlorine plasma yielded small etching rates, caused by chemical modifications of the sample surface which result in a passivation layer reducing the chemical etching rate. Using IBE, microstructures down to the 1 μm regime could be fabricated without reducing the critical temperature T_c and the critical current density J_c of the material. Etching rates up to 40 nm/min could be achieved without deteriorating the properties of the superconducting film by cooling the sample effectively during the etching process. The influence of the etching process on J_c was investigated by imaging the spatial distribution of the critical current along the patterned microstructures using Low-Temperature Scanning Electron Microscopy (LTSEM).     

High power-added-efficiency AlGaN/GaN HEMTs fabricated by atomic level controlled etching

An atomic-level controlled etching(ACE)technology is invstigated for the fabrication of recessed gate AlGaN/GaN high-electron-mobility transistors(HEMTs)with high power added efficiency.We compare the recessed gate HEMTs with conventional etching(CE)based chlorine,Cl₂-only ACE and BCl³/Cl₂ACE,respectively.The mixed radicals of BCl₃/Cl₂were used as the active reactants in the step of chemical modification.For ensuring precise and controllable etching depth and low etching damage,the kinetic energy of argon ions was accurately controlled.These argon ions were used precisely to remove the chemical modified surface atomic layer.Compared to the HEMTs with CE,the characteristics of devices fabricated by ACE are significantly improved,which benefits from significant reduction of etching damage.For BCl₃/Cl₂ACE recessed HEMTs,the load pull test at 17 GHz shows a high power added efficiency(PAE)of 59.8%with an output power density of 1.6 W/mm at Vd=10 V,and a peak PAE of 44.8%with an output power density of 3.2 W/mm at Vd=20 V in a continuous-wave mode.     

K负载Ce0.5Mn0.5O2催化剂对柴油机碳烟氧化性能的影响

采用柠檬酸络合法制备了不同KNO3负载量的xK-Ce_0.5Mn_0.5O₂系列催化剂,采用热重分析仪对其催化碳烟颗粒(PM)的活性进行评价,并用Coats-Redfern法进行氧化动力学分析,同时采用XRD,H2-TPR,Raman,XPS等技术对催化剂样品内部结构进行探究。结果表明:KNO₃负载使得少部分钾离子进入晶格内部,导致铈锰固溶体产生更多晶格缺陷,提高了催化剂中活性氧的含量。其余的KNO3则与Mn物种发生反应产生了具有更高催化活性的钾锰矿,改变了碳烟与催化剂的接触状态,提升了催化剂的活性。催化剂活性与KNO₃的负载量也有一定关系,当x=0.2时,催化剂的活性达到最佳,碳烟氧化所需要的活化能最低。     

不同钝化结构对非极性AlGaN-MSM紫外探测器性能的提升

在r面蓝宝石衬底上,采用金属有机化学气相沉积（MOCVD）法高温生长了未掺杂非极性AlGaN半导体薄膜,在此基础上制备了金属-半导体-金属（MSM）结构的紫外探测器。系统研究了在AlGaN半导体薄膜表面分别磁控溅射SiO₂纳米颗粒与SiO₂钝化层两种钝化手段对非极性AlGaN-MSM结构的紫外探测器性能的影响。实验结果表明：磁控溅射SiO₂纳米颗粒钝化或SiO₂钝化层两种手段都能提升AlGaN-MSM结构紫外探测器性能。暗电流测试表明,SiO₂纳米颗粒和SiO₂钝化层可使器件暗电流下降1~2个数量级,达到nA量级。光谱响应测试发现,在5 V偏压下,探测器在300 nm处具有陡峭的截止边,这表明其具有很好的深紫外特性,光谱响应提高了10³倍,紫外可见抑制比高达10⁵。     

Crystalline silicon surface passivation investigated by thermal atomic-layer-deposited aluminum oxide

Atomic-layer-deposited(ALD) aluminum oxide(Al_2O_3) has demonstrated an excellent surface passivation for crystalline silicon(c-Si) surfaces, as well as for highly boron-doped c-Si surfaces. In this paper, water-based thermal atomic layer deposition of Al_2O_3 films are fabricated for c-Si surface passivation. The influence of deposition conditions on the passivation quality is investigated. The results show that the excellent passivation on n-type c-Si can be achieved at a low thermal budget of 250℃ given a gas pressure of 0.15 Torr. The thickness-dependence of surface passivation indicates that the effective minority carrier lifetime increases drastically when the thickness of Al_2O_3 is larger than 10 nm. The influence of thermal post annealing treatments is also studied. Comparable carrier lifetime is achieved when Al_2O_3 sample is annealed for 15 min in forming gas in a temperature range from 400℃ to 450℃. In addition, the passivation quality can be further improved when a thin PECVD-SiN_x cap layer is prepared on Al_2O_3, and an effective minority carrier lifetime of2.8 ms and implied Voc of 721 mV are obtained. In addition, several novel methods are proposed to restrain blistering.     

A12o3钝化及其在晶硅太阳电池中的应用

介绍了A1203的材料性质及其原子层沉积制备方法,详细阐述了该材料的钝化机制（化学钝化和场效应钝化）,并从薄膜厚度、热稳定性及叠层钝化等角度阐释其优化方案．概述了Al203钝化在晶体硅太阳电池中的应用,主要包括钝化发射极及背面局部扩散电池和钝化发射极及背表面电池．最后,对A1203钝化工艺的未来研究方向和大规模的工业应用进行了展望．     

Etching mask optimization of InAs/GaSb superlattice mid-wavelength infared 640×512 focal plane array

In this paper we focused on the mask technology of inductively coupled plasma(ICP) etching for the mesa fabrication of infrared focal plane arrays(FPA).By using the SiO_2 mask,the mesa has higher graphics transfer accuracy and creates less micro-ripples in sidewalls.Comparing the IV characterization of detectors by using two different masks,the detector using the SiO_2 hard mask has the R_0A of 9.7×10~6 Ω·cm~2,while the detector using the photoresist mask has the R_0A of3.2 × 10~2 Ω·cm~2 in 77 K.After that we focused on the method of removing the remaining SiO_2 after mesa etching.The dry ICP etching and chemical buffer oxide etcher(BOE) based on HF and NH4 F are used in this part.Detectors using BOE only have closer R_0A to that using the combining method,but it leads to gaps on mesas because of the corrosion on AlSb layer by BOE.We finally choose the combining method and fabricated the 640×512 FPA.The FPA with cutoff wavelength of 4.8 μm has the average R_0A of 6.13 × 10~9 Ω·cm~2 and the average detectivity of 4.51 × 10~9 cm·Hz~(1/2).W~(-1)at 77 K.The FPA has good uniformity with the bad dots rate of 1.21%and the noise equivalent temperature difference(NEDT) of 22.9 mK operating at 77 K.     

Measurement of bulk etch rate of LR115 detector with atomic force microscopy

Equations for calculating track parameters have been proposed, which invariably involve the track etch rate V_t and the bulk etch rate V_b. The present study measured V_b for the LR115 solid-state nuclear track detector using atomic force microscopy (AFM). The detectors were partially masked using rubber cement and then etched in 2.5 N NaOH solution at 60°C for time periods ranging from 5 to 40 min. The rubber cement was then peeled off and cross-sectional images of the LR115 detectors were obtained by AFM. V_b has been found to have different values below and beyond the etching time of about 13.5 min, with the values of 0.0555 and 0.0875 μm min⁻¹, respectively. The increase in V_b with the etching time can be explained by a diffusion-etch model, in which the additional damage of the detector material is due to those etchant ions diffused into the detector over time. Now that V_b has been determined, this can be combined with the track etch rate V_t to calculate track parameters.     

Passivation and dissociation of Pb-type defects at a-SiO_2/Si interface

It is well known that in the process of thermal oxidation of silicon,there are P_b-type defects at amorphous silicon dioxide/silicon(a-SiO_2/Si) interface due to strain.These defects have a very important impact on the performance and reliability of semiconductor devices.In the process of passivation,hydrogen is usually used to inactivate P_b-type defects by the reaction P_b+H_2→P_bH+H.At the same time,P_bH centers dissociate according to the chemical reaction P_bH→P_b+H.Therefore,it is of great significance to study the balance of the passivation and dissociation.In this work,the reaction mechanisms of passivation and dissociation of the P_b-type defects are investigated by first-principles calculations.The reaction rates of the passivation and dissociation are calculated by the climbing image-nudged elastic band(CI-NEB)method and harmonic transition state theory(HTST).By coupling the rate equations of the passivation and dissociation reactions,the equilibrium density ratio of the saturated interfacial dangling bonds and interfacial defects(P_b,P_(b0),and P_(b1))at different temperatures is calculated.     

Energy loss dependent transversal etching rates of heavy ion tracks in plastic

By the method of electrolytical etching track etching rates V_t and corresponding transversal track etching rates V_trans of single heavy ion tracks in thin Makrofol KG foils have been measured at ion energies from 10–480 MeV/u. Makrofol KG foils of 8 μm thickness were irradiated perpendicular to the surface with ⁷⁹Au and ⁵⁴Xe ions at specific energies with energy loss values of REL=(10–90) ^*10³ MeVcm²/g at GSI Darmstadt, Germany, and Lawrence Berkeley Lab., Cal., USA. Using the electrolytical etching method by measuring the resistance of the foil during the etching process (etching conditions: 6n NaOH, room temperature and controlled 50° C) the breakthrough time and track etching rates V_t, V_trans and V_m (bulk etching rate) were analysed. Response curves (V_t/V_m)-1 as a function of Restricted Energy Loss (REL), the maximum extension of the ion induced damage perpendicular to the ion path and the dimension of the ion track core depending on the deposited energy can be estimated.     

Motion of Chern-Simons number at high temperatures under a chemical potential

I investigate the evolution of finite temperature, classical Yang-Mills field equations under the influence of a chemical potential for Chern-Simons number N_cs. The rate of N_cs diffusion,, Γ_d, and the linear response of N_cs to a chemical potential, Γ_μ, are both computed; the relation Γ_d = 2Γ_μ is satisfied numerically and the results agree with the recent measurement of Γ_d by Ambjørn and Krasnitz. The response of N_cs under chemical potential remains linear at least to μ = 6T, which is impossible if there is a free energy barrier to the motion of N_cs. The possibility that the result depends on lattice artefacts via hard thermal loops is investigated by changing the lattice action and by examining elongated rectangular lattices; provided that the lattice is fine enough, the result is weakly if at all dependent on the specifics of the cutoff. I also compare SU(2) with SU(3) and find Γ_SU(3) 7(_{s/w)⁴ΓSU(2)}.     

The mass-scale of supersymmetry breaking and proton decay

A fundamental mass-scale is associated with the transition of supersymmetric SU(3)_c×SU(2)_L×U(1) to the ordinary SU(3)_c×SU(2)_L×U(1) symmetry of elementary particle interactions. The renormalisation of the gauge coupling in a supersymmetric SU(5) grand unification leads to the mass-scale of supersymmetry breaking to be of order 10¹² GeV if the lifetime of the proton is taken to be 10³⁰ y and is lowered to the mass-scale of ordinary electroweak interactions if the proton lives longer than 10³⁰ y. It is lower than 10¹² GeV if the contribution of light scalars is taken into account. The predictions of the weak angle sin²θ (M_W) are in excellent agreement with experiment.     

Supersymmetric left-right model and its tests in linear colliders

We investigate phenomenological implications of a supersymmetric left-right model based on SU(2)_L × SU(2)_R × U(1)_B–L gauge symmetry testable in the next generation linear colliders. We concentrate in particular on the doubly charged SU(2)_R triplet higgsino , which we find very suitable for experimental search. We estimate its production rate in e⁺e⁻, e⁻e⁻, e⁻γ and γγ collisions and consider its subsequent decays. These processes have a clear discovery signature with a very low background from other processes.     

The Anomaly Coupling of Axigluon and Technicolor Neutral Pseudo Goldstone Bosons

By gauging the anomaly terms according to the gauge group SU(3)_cl x SU(3)_cr × SU(2)_l × U(l)_Y in the technicolor theory, we obtain various possibld anomaly vertices involving technicolor pseudo Goldstone boson and gauge boson (γ, Z, g, g_A). We estimate the decay rates of g_A → gP⁰, g_A → P_A⁰³γ and g_A → P_A⁰³Z.     

SiO2 passivation film effects on microwave characteristics of YBa2Cu3O7−x-based resonators

SiO₂ film coated as a passivation layer for YBa₂Cu₃O_7−x (YBCO)-based microwave devices is investigated by measuring the microwave characteristics of microstrip line resonators. The SiO₂ film is deposited with its 0.3 to 0.4 μm thickness by a sputtering method using Ar + 30%O₂ plasma. These deposition conditions do not degrade the microwave characteristics and the critical temperature (T_c). Next, the SiO₂ film coated resonators are compared with the uncoated ones for two kinds of degradation conditions: a 200°C annealing in air, and an exposure to air at 85°C and 85% RH (relative humidity). We find that the SiO₂ passivation film prevents the YBCO thin film from the surface degradation and reacting with water.     

The effect of etching solution composition on the response of an electrochemically etched CR-39 detector

Etching solutions of different compositions were applied at room temperature (22°C) for electrochemical etching. The background developed during electrochemical etching in a CR-39 track detector was investigated. Detectors irradiated with alphas of 5.49 MeV were measured also. It was found that the PEW solutions (potassiumhydroxid, ethylalcohol, water) showed good sensitivity. One of them (PEW_20/40 was applied for neutrons from a ²⁵²Cf source. The achieved registration sensitivity was about 10⁻⁵ spot/n after 3 hours of etching time.     

The SU(8) GUT for chiral families

We argue that there is a natural inclusion of the standard model with the family-unified chiral local symmetry SU(3)_H in a new SU(8) GUT inspired by Georgi's SU(11) model. The SU(8) symmetry breaking along the chain with the intermediate electro-weak-horizontal unification SU(8)→SU(5)_EWH×SU(3)_c×U(1) is proved d to be the distinguished pattern. The model predicts a long-lived proton (10³³–10³⁵yr) and practically the observed value of the Weinberg angle, in sharp contrast to the ordinary GUTs. The observation of the specific flavour-changing baryon decays (p→π,μ,Ke,…) could unambiguously single out the flavour unified GUTs as well as confirm the existence of the elementary horizontal forces at small distances.     

InGaAs/Si3N4 interface obtained in ultrahigh vacuum multipolar plasma: In-situ control by ellipsometry and electrical characterization

A multipolar plasma passivation scheme controlled by in-situ ellipsometry has been developed to produce a high electrical quality InGaAs/Si₃N₄ interface. We have demonstrated the possibility to remove all native oxides at the InGaAs surface by heating the sample at 240°C, then using the action of a multipolar H₂ plasma at 185°C, without optical degradation of the surface. The passivation by a native nitride layer is then performed using a N₂ plasma, and Si₃N₄ is deposited. The treatment induces a reduction of the density of interface states N_ss(E), and also a change of the nature of these interface states as shown by a reduction in the capture cross section σ_n(E).