In0.53Ga0.47As(1 0 0) native oxide removal by liquid and gas phase HF/H2O chemistries

The native oxide removal, surface termination, and stoichiometry of InGaAs(1 0 0) surfaces using liquid and gas phase HF/H₂O etching were studied using X-ray photoelectron spectroscopy. Oxide removal in liquid phase HF stopped at the As layer, producing either elemental or H-terminated As. The surface oxidized upon air exposure, forming a 4.8 Å As₂O₃ layer on an As rich InGaAs sub-surface (17% In, 16% Ga, 66% As). A sub atmospheric gas phase HF/H₂O process (100 Torr, 29 °C, 0.5 min) completely removed As₂O₃ and produced mainly In and Ga fluorides, since As fluoride is volatile at these experimental conditions. Once enough F accumulated on the surface, the water sticking probability decreased and the etching reaction proceeded at a much lower rate. The highest oxide removal (4.2 Å residual oxide) was achieved after 5 min of etching. As₂O₃ and As₂O₅ were completely removed and considerably more InF₃ and GaF₃ were produced. The surface contained a group III-fluoride rich overlayer (34% In, 36% Ga) on a slightly As rich bulk (21% In, 21% Ga, and 58% As). The As rich InGaAs sub-surface produced with both liquid and the longer gas phase HF treatments is intrinsic to HF-InGaAs chemistry, although the oxide removal mechanism is likely different.     

The structural and electrical properties of the SrTa2O6/In0.53Ga0.47As/InP system

The structural and electrical properties of SrTa₂O₆(SrTaO)/n-In_0.53GaAs_0.47(InGaAs)/InP structures where the SrTaO was grown by atomic vapor deposition, were investigated. Transmission electron microscopy revealed a uniform, amorphous SrTaO film having an atomically flat interface with the InGaAs substrate with a SrTaO film thickness of 11.2 nm. The amorphous SrTaO films (11.2 nm) exhibit a dielectric constant of ∼20, and a breakdown field of >8 MV/cm. A capacitance equivalent thickness of ∼1 nm is obtained for a SrTaO thickness of 3.4 nm, demonstrating the scaling potential of the SrTaO/InGaAs MOS system. Thinner SrTaO films (3.4 nm) exhibited increased non-uniformity in thickness. From the capacitance-voltage response of the SrTaO (3.4 nm)/n-InGaAs/InP structure, prior to any post deposition annealing, a peak interface state density of ∼2.3 × 10¹³ cm⁻² eV⁻¹ is obtained located at ∼0.28 eV (±0.05 eV) above the valence band energy (E_v) and the integrated interface state density in range E_v + 0.2 to E_v + 0.7 eV is 6.8 × 10¹² cm⁻². The peak energy position (0.28 ± 0.05 eV) and the energy distribution of the interface states are similar to other high-k layers on InGaAs, such as Al₂O₃ and LaAlO₃, providing further evidence that the interface defects in the high-k/InGaAs system are intrinsic defects related to the InGaAs surface.     

Direct measurement of interfacial structure in epitaxial Gd2O3 on GaAs (0 0 1) using scanning tunneling microscopy

The epitaxial growth of Gd₂O₃ on GaAs (0 0 1) has given a low interfacial density of states, resulting in the demonstration of the first inversion-channel GaAs metal-oxide-semiconductor field-effect transistor. Motivated by the significance of this discovery, in this work, cross-sectional scanning tunneling microscopy is employed herein to obtain precise structural and electronic information on these epitaxial films and interfaces. At the interface, the interfacial stacking of Gd₂O₃ films is directly correlated with the stacking sequence of the substrate GaAs. Additionally, from the local electronic states across the gate oxides, the spatial extent of the GaAs wavefunctions into the oxide dielectric may suggest a minimum Gd₂O₃ thickness to be of bulk properties.     

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.     

高峰谷电流比的高掺杂发射区In0.53Ga0.47As/AlAs共振隧穿二极管

利用空气桥工艺设计和制作了高掺杂发射区In0.53Ga0.47As/AlAs共振隧穿二极管（RTD）。在室温下,器件的峰谷电流比大于40,峰值电流密度为24kA/cm2。建立了RTD器件等效电路模型,并从直流和微波测试结果中提取出器件参数。高峰谷电流比的RTD器件具有非常小的电容,有利于在微波/太赫兹领域中的应用。     

Density functional theory study of first-layer adsorption of ZrO2 and HfO2 on Ge(1 0 0)

Density functional theory was used to performed a survey of transition metal oxide (MO₂ = ZrO₂, HfO₂) ordered molecular adsorbate bonding configurations on the Ge(1 0 0)-4 × 2 surface. Surface binding geometries of metal-down (O-M-Ge) and oxygen-down (M-O-Ge) were considered, including both adsorbate and displacement geometries of M-O-Ge. Calculated enthalpies of adsorption show that bonding geometries with metal-Ge bonds (O-M-Ge) are essentially degenerate with oxygen-Ge bonding (M-O-Ge). Calculated electronic structures indicate that adsorbate surface bonding geometries of the form O-M-Ge tend to create a metallic interfaces, while M-O-Ge geometries produce, in general, much more favorable electronic structures. Hydrogen passivation of both oxygen and metal dangling bonds was found to improve the electronic structure of both types of MO₂ adsorbate systems, and induced the opening of true semiconducting band gaps for the adsorbate-type M-O-Ge geometries. Shifts observed in the DOS minima for both O-M-Ge and M-O-Ge adsorbate geometries are consistent with surface band bending induced by the adsorbate films, where such band bending extends much further into the Ge substrate than can be modeled by the Ge slabs used in this work.     

Characteristics of a In0.52(AlxGa1-x)0.48As/In0.53Ga0.47As(0⩽x⩽1) heterojunction and its application onHEMT's

The quaternary In_0.52(Al_xGa_1-x) _0.48As compound on InP substrates is an important material for use in optoelectronic and microwave devices. We systematically investigated the electrical properties of quaternary In_0.52(Al_xGa_1-x)_0.48As layers, and found a 10% addition of Ga atoms into the InAlAs layer improves the Schottky diode performance. The energy bandgap (E_g ) for the In_0.52(Al_xGa_1-x)_0.48As layer was (0.806+0.711x) eV, and the associated conduction-band discontinuity (ΔE_c), in the InAlGaAs/In_0.53Ga_0.47 As heterojunction, was around (0.68±0.01)ΔE_g . Using this high quality In_0.52(Al_0.9Ga_0.1)_0.48As layer in the Schottky and buffer layers, we obtained quaternary In_0.52(Al_0.9Ga_0.1)_0.48As/In _0.53Ga_0.47As HEMTs. This quaternary HEMT revealed excellent dc and microwave characteristics. In comparison with the conventional InAlAs/InGaAs HEMT's, quaternary HEMT's demonstrated improved sidegating and device reliability     

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.     

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.     

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.     

Design and experimental characteristics of strained In0.52Al0.48As/InxGa1-xAs (x>0.53)HEMTs

Strained In_0.52Al_0.48 As/In_xGa _1-xAs (x>0.53) HEMTs (high electron mobility transistors) are studied theoretically and experimentally. A device design procedure is reported that is based on band structure and charge control self-consistent calculations. It predicts the sheet carrier density and electron confinement as a function of doping and thickness of layers. The DC performance at 300 K is presented. Wafer statistics demonstrate improvement of device characteristics with excess indium in the channel (g¯_{m, intr}=500 and 700 mS/mm for x=0.60 and 0.65). Microwave characterization shows the f_T improvement (f_T=40 and 45 GHz for x=0.60 and 0.65, respectively) and the R_ds limitations of the 1-μm-long-gate HEMTs     

Heteroepitaxy of In0.53Ga0.47As on GaAs substrate by low pressure metalorganic chemical vapor deposition for the OEIC applications

InP/In_0.53Ga_0.47As/InP sandwich structure grown by low pressure metalorganic chemical vapor deposition has been investigated, in order to assess the different heteroepitaxy schemes which are based on low temperature (LT) InP metamorphic buffer layer. Photoluminescence (PL) and high resolution X-ray diffraction (HRXRD) and scan probe microscope (SPM) have been carried out to characterize the heteroepitaxy samples. For the best optimum growth condition of 15 nm-thick LT InP buffer at the growth temperature of 450 °C, the full width at half maximum (FWHM) values of the HRXRD, the room-temperature PL were 512 arcsec and 51.7 meV, respectively and the root mean square of SPM is only 0.915 nm.     

In0.52Al0.48As/InxGa1-xAs (0.53⩽x⩽0.70) lattice-matched and strainedheterostructure insulated-gate FETs

The DC and microwave properties of In_0.52Al_0.48 Al/In_xGa_1-xAs (0.53⩽x⩽0.70) heterostructure insulated gate field-effect transistors (HIGFETs) with a quantum well channel design are presented. DC and microwave transconductances (g_m) are enhanced as the In content is increased in the InGaAs channel. An intrinsic microwave g _m value of 428 mS/mm and a K-factor of 1140 mS/mm-V have been obtained for 1.0-μm gate length with the 65% In channel devices. The sheet charge density, drift mobility, transconductance, current-gain cutoff frequency (f_T), and maximum oscillation frequency (f _max) all show a continuous improvement up to 65% In content ( f_T=22.5 GHz with 53% and f_T=27 GHz with 65% In; the corresponding f_max change is from 6.5 to 8 GHz). The device performance degrades as the In content is increased to 70%. DC and microwave characteristics show the presence of negative differential resistance (NDR) up to 2.7 GHz     

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.     

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。     

Photoemission study of the Si(1 1 1)-native SiO2/copper phthalocyanine (CuPc) ultra-thin film interface

The Ultraviolet and X-ray Photoemission Spectroscopy (UPS, XPS) investigation was done to examine the interface formation between deposited copper phthalocyanine (CuPc) thin films and covered with native oxide n- and p-type silicon Si(1 1 1) substrates. The UPS results indicated the existence of small interface dipole effect for very first layer of CuPc deposited on both types of substrates. The dipoles were oriented differently depending on silicon conductivity type. In this paper we present that near the inorganic/organic interface the phthalocyanine’s molecular orbital levels shift downwards 0.20 ± 0.05 eV in the case of n-Si substrate and upwards 0.25 ± 0.05 eV for p-Si indicating the different displacement of the negative charge within the interface region. This tendency was also confirmed by conducted XPS study of the core levels. It is highly probable that band bending-like shift is provoked by the continuous change of CuPc molecule orientation induced by interface polarization layer.     

Single and dual p-doped channel In0.52Al0.48As/InxGa1-xAs (x=0.53, 0.65) FET's andthe role of doping

The properties of lattice-matched (x=0.53) and strained ( x=0.65) In_0.52Al_0.48As/In_xGa _1-xAs p-doped channel FETs are reported. The role of doping density is studied with the help of two designs (dual-channel with low doping and single-channel with high doping). The strained dual-channel devices demonstrated an improvement of mobility from 108 cm²/V-s (53% In) to 265 cm²/V-s (65% In) at 300 K. The corresponding intrinsic transconductance enhancement is from 23 Ms/mm (53% In) to 46.5 mS/mm (65% In) using 1.0 μm-long gates. The cutoff frequency (f_t) also improves from 1.0 to 1.4 GHz. The impact of strain in the highly-doped single-channel device is small. The band structure under lattice-matched and strained conditions and the position of the Fermi level according to doping seem to be the main factors determining the reported features     

Characteristics of 0.8- and 0.2-μm gate length InxGa1-xAs/In0.52Al0.48As/InP(0.53⩽x⩽0.70) modulation-doped field-effect transistorsat cryogenic temperatures

The performance characteristics of InP-based pseudomorphic MODFETs with varying the In composition (0.53⩽x⩽0.70), which changes the strain in the channel, were studied. The temperature was varied in the range of 40-300 K, and the devices had gate lengths L _g of 0.8 and 0.2 μm. The analysis predicts an increase in the intrinsic cutoff frequency with increasing In composition and decreasing temperature and gate length. Also, the analysis predicts that the increase in cutoff frequency with decreasing temperature is less significant with increasing In composition and decreasing gate length. Preliminary experimental results show that as In composition increases from 0.53 to 0.70, f_T increases by 30-40%, and as the temperature decreases from 300 to 40 K, f_T improves by 15-30%, both for 0.8- and 0.2-μm devices     

Piezoelectricity and carrier dynamics in In0·2Ga0·8As/GaAs single quantum wells grown on (n11)A-oriented GaAs (n=1, 2, 3)

Temporal variations of the photoluminescence (PL) peak wavelength due to screening of the piezoelectric field by photogenerated carriers are observed in ln_0·2Ga_0·8As/GaAs single quantum wells grown on (n11)A-oriented substrates (n=1, 2, 3) by using time-resolved PL spectroscopy. The partial screening of the piezoelectric field shifts the PL peak to shorter wavelengths. The subsequent decrease of the photogenerated carriers by recombination produces a redshift of the PL peak, which is explained using a model that fits successfully the experimental results.     

H2S molecular beam passivation of Ge(0 0 1)

A fundamental issue regarding the introduction of high-mobility Ge channels in CMOS circuits is the electrical passivation of the interface with the high-k gate dielectric. In this paper, we investigate the passivation of p-Ge(0 0 1) using molecular H₂S. The modification of the semiconductor surface is monitored in situ by RHEED and the interface is characterized by XPS analyses. MOS capacitors are fabricated to extract interface state density, and finally we demonstrate the efficiency of the passivation scheme using a combination with an ultra thin Al interlayer.