Al2O3 stacks on In0.53Ga0.47As substrates: In situ investigation of the interface

In this work we present an in situ investigation of the interface composition between an In_0.53Ga_0.47As substrate and an Al₂O₃ oxide grown by molecular beam deposition in ultra high vacuum conditions. In the effort to improve the chemical quality of the interface, reduction of semiconductor-oxygen bonding at the interface can be obtained by growing a few Å thick pure Al layer before starting exposure of the surface to the atomic oxygen flux. Conversely, when a Ge interface passivation layer is intercalated between the semiconductor and the oxide stack, the interface chemistry is governed by Ge reaction with other species (Al, O), leading only to a partial suppression of the interface oxides.     

Effects of surface passivation during atomic layer deposition of Al2O3 on In0.53Ga0.47As substrates

In this work we investigate the effect of different III-V surface passivation strategies during atomic layer deposition of Al₂O₃. X-ray photoelectron spectroscopy indicates that bare As-decapped and sulfur passivated In_0.53Ga_0.47As present residual oxides on the surface just before the beginning of the Al₂O₃ deposition while the insertion of a Ge interface passivation layer results in an almost oxide free Ge/III-V interface. The study of the initial growth regimes, by means of in situ spectroscopic ellipsometry, shows that the growth of Al₂O₃ on Ge leads to an enhanced initial growth accompanied by the formation of Ge-O-Al species thus affecting the final electrical properties of the stack. Alternatively, deposition on decapped and S-passivated In_0.53Ga_0.47As results in a more controlled growth process. The sulfur passivation leads to a better electrical response of the capacitor that can be associated to a lower oxide/semiconductor interface trap density.     

Remote phonon and surface roughness limited universal electron mobility of In0.53Ga0.47As surface channel MOSFETs

The inversion layer electron mobility in n-channel In_0.53Ga_0.47As MOSFET’s with HfO₂ gate dielectric with several substrate impurity concentrations (∼1 × 10¹⁶ cm⁻³ to ∼1 × 10¹⁸ cm⁻³) and various surface preparations (HF surface clean, (NH₄)₂S surface clean and PECVD a-Si interlayer with a HfO₂ gate dielectric) have been studied. The peak electron mobility is observed to be strongly dependent on the surface preparation, but the high field mobility is observed to be almost independent of the surface preparation. A detailed analysis of the effective mobility as a function of electric field, substrate doping, and temperature was used to determine the various mobility components (surface roughness, phonon, and coulombic scattering limited mobility components). For the substrates with high doping concentration, the electron mobility at low vertical electric field is dominated by Coulomb scattering from the substrate dopants, whereas, for lower substrate doping the Coulombic scattering is dominated by the disorder induced gap states. Low temperature measurements were used to determine the surface roughness scattering and phonon components. The results show that room temperature mobility of In_0.53Ga_0.47As surface channel MOSFETs with HfO₂ gate dielectric at high electric field is limited primarily by remote phonons whereas the Al₂O₃ gate dielectric is limited by surface roughness scattering.     

Analysis of the dark current and photoresponse of In0.53Ga0.47As/InP avalanche photodiodes

The doping profiles, current-voltage (I–V) and photoresponse characteristics of five In_0.53Ga_0.47As/InP avalanche photodiode (APD) wafers are presented. A detailed analysis indicates that the dark current is due largely to generation and recombination of carriers in the diode bulk, and in some wafers tunneling at the p-n junction is dominant near breakdown (V_B). In some cases, significant surface currents are also observed. In three high-performance wafers, however, low primary dark currents (～5 nA) with no evidence for tunnelling at 0.99 V_B have been obtained. In addition, microplasmas have been found in some wafers, due to local breakdown possibly arising from crystalline defects. Nevertheless, we report uniform gains as high as 100. The dark current and gain characteristics of these devices are among the best reported to date for In_0.53Ga_0.47As/InP APDs.Finally, the response of the APDs to fast optical pulses has been analyzed at both low and high illumination intensity. The slow speed of response, which has been reported elsewhere, is considered in detail and is found to be due to charge pile-up at the abrupt n-In_0.53Ga_0.47As/n-InP heterointerface which is characteristic of our devices. Using an analysis of the response time thermal activation energy along with the transient pulse shape, we infer that the heterointerfaces are graded over a length of $\text{2}\text{L}\text{≌ 300}\text{A}\text{?}$. The model predicts that fast response can be obtained for heterointerface grading lengths of $\text{2}\text{L}\text{? 500}\text{A}\text{?}$, depending on the epitaxial layer doping and extent of penetration of the depletion region into the In_0.53Ga_0.47As layer at breakdown.     

Improving electrical characteristics of W/HfO2/In0.53Ga0.47As gate stacks by altering deposition techniques

The effects of controlling InGaAs substrate temperature during electron beam deposition of HfO₂ on electrical characteristics of W/HfO₂/n-In_0.53Ga_0.47As capacitors are investigated. It is found that by depositing a thin HfO₂ layer at the interface when substrate temperature is raised to 300 °C, frequency dispersion at depletion and accumulation conditions is reduced and interface state density is lowered regardless of the HfO₂ thickness. Cross-sectional transmission electron microscopy images have revealed that the formation of mesoscopic voids in the InGaAs substrate near the interface is suppressed with HfO₂deposition at 300 °C at the interface. A band diagram with an additional bulk trap energy level has been proposed to explain the frequency dispersion and conductance peaks at accumulation condition.     

In0.53Ga0.47As表面氮化和硫钝化对其Al/Al2O3/InGaAs MOS电容特性的影响

本文通过对比频散特性和滞回特性,计算界面态密度D_it和有效边界缺陷密度ΔN_bt,分析界面缺陷和漏电流等方法,系统的研究了In_0.53Ga_0.47As表面氮化和硫钝化对其Al/Al₂O₃/InGaAs结构MOS电容特性的影响。实验结果表明,这两种方法都能够在InGaAs表明形成一层界面钝化层。相比较于未处理的样品,经过氮气等离子体处理的样品表现出较好的界面特性,得到了最小的积累区频散、滞回电压,以及良好的I-V性能。经过(NH₄)₂S_x处理的样品则获得了最小的平带电压区频散以及最低的界面态密度Dit=2.6E11cm_-2eV_-1.     

Interface state densities, low frequency noise and electron mobility in surface channel In0.53Ga0.47As n-MOSFETs with a ZrO2 gate dielectric

This paper reports on an investigation of interface state densities, low frequency noise and electron mobility in surface channel In_0.53Ga_0.47As n-MOSFETs with a ZrO₂ gate dielectric. Interface state density values of D_it ∼ 5 × 10¹² cm⁻² eV⁻¹ were extracted using sub-threshold slope analysis and charge pumping technique. The same order of magnitude of trap density was found from low frequency noise measurements. A peak effective electron mobility of 1200 cm²/Vs has been achieved. For these surface channel In_0.53Ga_0.47As n-MOSFETs, it was found that η parameter, an empirical parameter used to calculate the effective electric field, was ∼0.55, and is to be comparable to the standard value found in Si device.     

InP基PIN型探测器中接触层掺杂对In_(0.53)Ga_(0.47)As材料光致发光特性的影响

利用MOCVD在InP衬底上制备InP/In0.53Ga0.47As/InP双异质结PIN型材料,通过对本征层In0.53Ga0.47As材料的光致荧光谱研究,发现PIN结构中两侧InP材料的掺杂特性对中间In0.53Ga0.47As材料的光致发光特性有明显的影响。本文通过对两侧InP材料的变掺杂处理,实现了In0.53Ga0.47As材料光致发光特性的有效提高。     

Electrical properties and interfacial chemical environments of in situ atomic layer deposited Al2O3 on freshly molecular beam epitaxy grown GaAs

Interfacial chemical analyses and electrical characterization of in situ atomic layer deposited (ALD) Al₂O₃ on freshly molecular beam epitaxy (MBE) grown n- and p- GaAs (001) with a (4 × 6) surface reconstruction are performed. The capacitance-voltage (C-V) characteristics of as-deposited and 550 °C N₂ annealed samples are correlated with their corresponding X-ray photoelectron spectroscopy (XPS) interfacial analyses. The chemical bonding for the as-deposited ALD-Al₂O₃/n- and p-GaAs interface is similar, consisting of Ga₂O (Ga¹⁺) and As-As bonding (As⁰) without any detectable arsenic oxides or Ga₂O₃; the interfacial chemical environments remained unchanged after 550 °C N₂ annealing for 1hr. Both as-deposited and annealed p-GaAs metal-oxide-semiconductor capacitors (MOSCAPs) exhibit C-V characteristics with small frequency dispersion (<5%). In comparison, n-GaAs MOSCAPs shows much pronounced frequency dispersion than their p-counterparts.     

Interface composition of atomic layer deposited HfO2 and Al2O3 thin films on InAs studied by X-ray photoemission spectroscopy

We present a synchrotron-based XPS investigation on the interface between InAs and Al₂O₃ or HfO₂ layers, deposited by ALD at different temperatures, for InAs substrates with different surface orientations as well as for InAs nanowires. We reveal the composition of the native Oxide and how the high-κ layer deposition reduces Oxide components. We demonstrate some of the advantages in using synchrotron radiation revealing the variation in Oxide composition as a function of depth into the subsurface region and how we can indentify Oxides even on nanowires covering only a small fraction of the surface.     

Correlation between the structural, morphological, optical, and electrical properties of In2O3 thin films obtained by an ultrasonic spray CVD process

Indium oxide (In₂O₃) thin films are successfully deposited on glass substrate at different deposition times by an ultrasonic spray technique using Indium chloride as the precursor solution; the physical properties of these films are characterized by XRD, SEM, and UV-visible. XRD analysis showed that the films are polycrystalline in nature having a cubic crystal structure and symmetry space group Ia3 with a preferred grain orientation along the (222) plane when the deposition time changes from 4 to 10 min, but when the deposition time equals 13 min we found that the majority of grains preferred the (400) plane. The surface morphology of the In₂O₃ thin films revealed that the shape of grains changes with the change of the preferential growth orientation. The transmittance improvement of In₂O₃ films was closely related to the good crystalline quality of the films. The optical gap energy is found to increase from 3.46 to 3.79 eV with the increasing of deposition time from 4 to 13 min. The film thickness was varied between 395 and 725 nm. The film grown at 13 min is found to exhibit low resistivity (10^-2 Ω·cm), and relatively high transmittance (~ 93%).     

Effect of In content of the buffer layer on crystalline quality and electrical property of In0.82Ga0.18As/InP grown by LP-MOCVD

The In_0.82Ga_0.18As grown on InP (1 0 0) substrates by low pressure metalorganic chemical vapor deposition (LP-MOCVD) with two-step growth method was investigated. It was analyzed that the effect of In content of buffer layer on the crystalline quality and electrical property of the In_0.82Ga_0.18As eplialyers, which were characterized by X-ray diffraction, scanning electron microscopy, and Hall effect. The experiments show that the crystalline quality and the electrical property of the In_0.82Ga_0.18As eplialyers have close relation to the In content of buffer layer and will be optimum when the In content of buffer layer is same as that of the epilayer.     

Effect of thickness on the structural,optical and electrical properties of RF magnetron sputtered GZO thin films

Gallium-doped zinc oxide (GZO) thin films with very high conductivity and transparency were successfully deposited by RF magnetron sputtering at a substrate temperature of 400 °C. The dependence of the film properties over the thickness was investigated. X-ray diffraction (XRD) results revealed the polycrystalline nature of the films with hexagonal wurtzite structure having preferential orientation along [001] direction normal to the substrate. The lowest resistivity obtained from electrical studies was 5.4×10⁻⁴ Ω cm. The optical properties were studied using a UV–vis spectrophotometer and the average transmittance in the visible region (400–700 nm) was found to be 92%, relative to the transmittance of a soda–lime glass reference for a GZO film of thickness 495 nm and also the transparency of the films decreases in the near IR region of the spectra. The mobility of the films showed a linear dependence with crystallite size. GZO film of thickness 495 nm with the highest figure of merit indicates that the GZO film is suitable as an ideal transparent conducting oxide (TCO) material for solar cell applications.     

Sn掺杂对(In0.95-xSnxFe0.05)2O3薄膜的结构、电学及磁特性的影响

我们利用脉冲激光沉积的方法制备了一系列(In0.95-xSnxFe0.05)2O3 (x=0~0.09)薄膜,并在其中发现了室温铁磁性。X射线衍射结果表明锡与铁离子已掺入氧化铟晶格。随着锡的掺入,样品内的载流子浓度得到了很大的提高,但相应的铁磁性却几乎没有变化。我们认为氧空位相关的束缚磁极化子模型能够跟好的解释我们的铁掺杂氧化铟薄膜中的铁磁耦合的机制,而载流子传导的RKKY相互作用则不适用于这一系统。     

Effect of ytterbium doping on the optical and electrical properties of intrinsic In2O3 thin films

Ytterbium doped In₂O₃ thin films (0.5%, 1.0%, 1.4%, 1.7% and 8.5 wt.%) have been prepared by a vacuum evaporation method on glass and silicon-wafer substrates. The prepared films were characterised by X-ray fluorescence, X-ray diffraction, UV-VIS-NIR absorption spectroscopy, and electrical (ac and dc) measurements. Experimental data indicate that Yb³⁺ doping slightly stress the In₂O₃ crystalline structure and change the optical and electrical properties. The electrical and optical behaviours of the Yb-doped In₂O₃ films show that they are wide-band semiconductors with band gap 3.67-3.7 eV and insulating properties. The ac and dc-electrical measurements show that it is possible to use Yb-doped In₂O₃ as an optical-sensitive high-k insulator for metal-insulator-silicon configurations.     

Effect of Sn-doping on the structural,electrical and magnetic properties of(In0.95-xSnxFe0.05)2O3 films

Room-temperature ferrornagnetism was observed in(In_0.95-xSn_xFe_0.05)₂O₃（x = 0-0.09） films deposited by pulsed laser deposition.XRD results give a direct proof that both Sn and Fe ions have been incorporated into the In₂O₃ lattice.The carrier concentration in the films is obviously increased by the Sn-doping,while the ferromagnetic properties are rarely changed.We think that in our Fe-doped In₂O₃ films,the oxygen vacancy-related bound magnetic polaron model,rather than the carrier-mediated RKKY coupling,is the main mechanism for the observed ferromagnetism.     

Influence of oxidation temperature on the microstructure and electrical properties of Ta2O5 on Si

The effect of the oxidation temperature (673-873 K) on the microstructural and electrical properties of thermal Ta₂O₅ thin films on Si has been studied. Auger electron spectroscopy and X-ray photoelectron spectroscopy results revealed that the films are non-stoichiometric in the depth; an interfacial transition layer between tantalum oxide and Si substrate, containing presumably SiO₂ was detected. It has been found by X-ray diffraction that the amorphous state of Ta₂O₅ depends on both the oxidation temperature and the thickness of the films—the combination of high oxidation temperature (>823 K) and thickness smaller than 50 nm is critical for the appearance of a crystal phase. The Ta₂O₅ layers crystallize to the monoclinic phase and the temperature of the phase transition is between 773 and 823 K for the thinner layers (<50 nm) and very close to 873 K for the thicker ones. The electrical characterization (current/voltage; capacitance/voltage) reveals that the optimal oxidation temperature for achieving the highest dielectric constant (∼32) and the lowest leakage current (10⁻⁸ A/cm² at 1 MV/cm applied field) is 873 K. The results imply that the poor oxidation related defects are rather the dominant factor in the leakage current than the crystallization effects.     

Fabrication of tunable [Al2O3:Alucone] thin-film encapsulations for top-emitting organic light-emitting diodes with high performance optical and barrier properties

The optical and barrier properties of thin-film encapsulations (TFEs) for top-emitting organic light-emitting diodes (TEOLEDs) were investigated using TFEs fabricated by stacking multiple sets of inorganic–organic layers. The inorganic moisture barrier layers were prepared by atomic layer deposition (ALD) of Al₂O₃ using trimethylaluminum (TMA) and O₃ as precursors and are shown to be efficient barriers against gases and vapors. The organic alucone layers were produced by molecular layer deposition (MLD) using TMA and ethylene glycol as precursors. The [Al₂O₃:Alucone] ALD/MLD films were used because their adjustable inorganic–organic nanolaminate composition allows for the tuning of the optical properties, thereby enhancing their application potential for the design and fabrication of high performance light out-coupling structures for TEOLEDs. By carefully adjusting the relative thickness ratio of the inorganic–organic encapsulation materials, optimized light extraction was achieved and the films not only maintained their high moisture barrier strength but also showed excellent optical performance.     

（英）沉积温度对脉冲激光沉积法在YSZ (100)衬底上生长的Mn1.56Co0.96Ni0.48O4尖晶石薄膜结构、电学和磁学性能的影响

在YSZ（100）衬底上,采用脉冲激光沉积法在500℃至700℃的不同沉积温度下生长出尖晶石结构的Mn_1.56Co_0.96Ni_0.48O₄（MCNO）薄膜.由于沉积温度是制备高质量薄膜的重要因素,本文研究了MCNO薄膜结构、电学和磁学性能随沉积温度的变化.通过对X射线衍射图和原子力显微镜图像的分析,发现MCNO薄膜的结晶与沉积温度有很大关系.随着沉积温度的升高,MCNO薄膜的电阻率呈V型变化,其导电过程可以用小极化子跳跃机理来描述.同时,随温度变化的磁化曲线表明所有样品都显示出从铁磁性到顺磁性的转变,且沉积温度为600℃的MCNO薄膜具有216 K的高居里温度.以上研究结果表明,在600℃沉积的MCNO薄膜具有适用于热敏电阻器件和多功能异质结所需的良好性能.