Drift velocity of electrons in quantum wells of selectively doped In0.5Ga0.5As/AlxIn1 ? xAs and In0.2Ga0.8As/AlxGa1 ? xAs heterostructures in high electric fields

The field dependence of drift velocity of electrons in quantum wells of selectively doped In_0.5Ga_0.5As/Al _x In_{1 − x} As and In_0.2Ga_0.8As/Al _x Ga_{1 − x} As heterostructures is calculated by the Monte Carlo method. The influence of varying the molar fraction of Al in the composition of the Al _x Ga_{1 − x} As and Al _x In_{1 − x} As barriers of the quantum well on the mobility and drift velocity of electrons in high electric fields is studied. It is shown that the electron mobility rises as the fraction x of Al in the barrier composition is decreased. The maximum mobility in the In_0.5Ga_0.5As/In_0.8Al_0.2As quantum wells exceeds the mobility in a bulk material by a factor of 3. An increase in fraction x of Al in the barrier leads to an increase in the threshold field E _th of intervalley transfer (the Gunn effect). The threshold field is E _th = 16 kV/cm in the In_0.5Ga_0.5As/Al_0.5In_0.5As heterostructures and E _th = 10 kV/cm in the In_0.2Ga_0.8As/Al_0.3Ga_0.7As heterostructures. In the heterostructures with the lowest electron mobility, E _th = 2–3 kV/cm, which is lower than E _th = 4 kV/cm in bulk InGaAs.     

Electron mobility and effective mass in composite InGaAs quantum wells with InAs and GaAs nanoinserts

The paper is concerned with the theoretical and experimental studies of the band structure and electrical properties of InAlAs/InGaAs/InAlAs/InP heterostructures containing a composite InGaAs quantum well with InAs and GaAs nanoinserts. From the Shubnikov-de Haas effect, the effective cyclotron mass m _c ^* is determined experimentally and calculated with consideration for the nonparabolicity of the electron energy spectrum. An approach to estimation of the effective mass is proposed and tested. The approach is based on weighted averaging of the m _c ^* of the composite quantum well’s constituent materials. A first proposed heterostructure containing two InAs inserts symmetrically arranged in the quantum well makes a 26% reduction in m _c ^* compared to m _c ^* in the lattice-matched In_0.53Ga_0.47As quantum well possible.     

Maximum drift velocity of electrons in selectively doped InAlAs/InGaAs/InAlAs heterostructures with InAs inserts

The dependence of the electron mobility and drift velocity on the growth conditions, thickness, and doping of an InAs insert placed at the center of the quantum well in a selectively doped InAlAs/InGaAs/InAlAs heterostructure has been investigated. Record enhancement of the maximum drift velocity to (2–4) × 10⁷ cm/s in an electric field of 5 × 10³ V/cm has been obtained in a 17-nm-wide quantum well with an undoped 4-nm-thick InAs insert. In the structures with additional doping of the InAs insert, which facilitates an increase in the density of electrons in the quantum well to 4.0 × 10¹² cm^?2, the maximum drift velocity is as high as 2 × 10⁷ cm/s in an electric field of 7 × 10³ V/cm.     

InGaAs/InP heterostructures with strained quantum wells and quantum dots (λ=1.5–1.9 µm)

Strongly strained In_xGa_1−x As/In_0.53Ga_0.47As/InP heterostructures with indium content x=0.69−1.0 in the active region were investigated experimentally and theoretically. Two types of structures were obtained by vapor-phase epitaxy from metalorganic compounds: 1) with isolated compression-strained quantum wells and 2) with self-organized nanosize InAs clusters (quantum dots). The temperature dependence of the quantum radiation efficiency of samples with quantum wells in the temperature range 77–265 K is characterized by T ₀=43 K. One reason for the low value of T ₀ is electron delocalization in the active region. The maximum radiation wavelength obtained in structures with quantum dots is 1.9 μm at 77 K. Fiz. Tekh. Poluprovodn. 33, 1105–1107 (September 1999)     

Effect of structural parameters on InGaAs/InAlAs 2DEG transport characteristics

The effect of structural parameters on the transport characteristics from 15 to 300 K of molecular beam epitaxy-grown InGaAs/InAlAs two dimensional electron gas structures lattice-matched to InP is determined. The InAlAs buffer layer thickness was varied from 1000 to 10,000Å. One sample also incorporated a InGaAs/InAlAs superlattice. The buffer layer thickness and structure had almost no effect on the mobility or sheet density. The InAlAs spacer layer was varied from 25 to 200Å. Increases in the InAlAs spacer thickness resulted in a monotonically decreasing sheet density and a peak in the mobility versus spacer thickness at 100Å. The highest 77 K mobility was 66,700 cm²/V/sds withN _D =1.2×10¹² cm^?2. The effect of illumination and temperature on the sheet concentration in these structures as well as on “bulk” InAlAs:Si was much smaller than in Al _x Ga_1?x As/GaAs structures or “bulk” Al _x Ga_1?x As, forx?0.30, indicating that devices based on this material system will not be characterized by many of the device instabilities observed in the AlGaAs/GaAs system.     

Highly confined two-dimensional electron gas in an In0.52AI0.48As/In0.52Ga0.47As modulation-doped structure with a strained InAs quantum well

This paper examines a detailed analysis by Shubnikov-de Haas measurements of the effective mass of two-dimensinal electron gas (2DEG) in an In_0.52Al_0.48As/ In_0.53Ga_0.47As modulation-doped (MD) structure with an InAs quantum well inserted into the InGaAs channel (InAs-inserted channel). The measured effec-tive mass of 2DEG in the InAs-inserted-channel MD structure is in good agreement with the calculated one of the strained InAs layer on In_0.53Ga_0.47As. This indicates that almost all of the 2DEG forms in the strained InAs quantum well. These results show that the InAs-inserted-channel MD structure improves the electron confinement, since the 2DEG is confined in the InAs quantum well with the thickness of 4 nm.     

Self-organized nanoscale InP islands in an InGaP/GaAs host and InAs islands in an InGaAs/InP host

Arrays of strained nanoscale InP islands in an In_0.49Ga_0.51P host on a GaAs(100) substrate and InAs islands in a In_0.53Ga_0.47As host on an InP(100) substrate are obtained by metalorganic vapor-phase epitaxy (MOVPE). Their structural and photoluminescence properties are investigated. It is shown that the nanoscale islands that are formed measure 80 nm (InP/InGaP) and 25–60 nm (InAs/InGaAs). The photoluminescence spectra of the nanoscale islands display bands in the wavelength ranges 0.66–0.72 and 1.66–1.91 μm at 77 K with maxima whose position does not vary as the effective thickness of InP and InAs increases. The radiation efficiency of the nanoscale InP islands is two orders of magnitude greater than the luminescence intensity of the InAs islands. Fiz. Tekh. Poluprovodn. 33, 858–862 (July 1999)     

Metamorphic modulation-doped InAlAs/InGaAs/InAlAs heterostructures with high electron mobility grown on gaas substrates

Metamorphic modulation-doped InGaAs/InAlAs heterostructures have been MBE-grown on GaAs substrates. The optimization of low-temperature growth conditions for a graded-composition buffer layer made it possible to reduce the amount of structural defects in the active layers of the structure. The electron mobility in the 2D channel of metamorphic structures grown under optimum conditions (8100 cm²/V s at 300 K) noticeably exceeds the values achievable in strained InGaAs/AlGaAs heterostructures on GaAs substrates.     

High electron mobility 18300 cm2/V·s in the InAIAs/lnGaAs pseudomorphic structure obtained by channel indium composition modulation

The highest electron mobility yet reported for an InP-based pseudomorphic structure at room temperature, 18300 cm²/V·s, has been obtained by using a structure with an indium composition modulated channel, namely, In_0.53Ga_0.47As/ In_0.8Ga_0.2As/InAs/In_0.8Ga_0.2As/In_0.53Ga_0.47As. Although the total thickness of the high In-content layers (In_0.8Ga_0.2As/InAs/In_0.8Ga_0.2As) exceeds the critical thick-ness predicted by Matthews theory, In_0.8Ga_0.2As insertion makes it possible to form smooth In_0.53Ga_0.47As/In_0.8Ga_0.2As and In_0.8Ga_0.2As/InAs heterointerfaces. This structure can successfully enhance carrier confinement in the high In-content layers. This superior carrier confinement can be expected to lead to the highest yet reported electron mobility.     

Technology and electronic properties of PHEMT AlGaAs/In y(z)Ga1 − y(z)As/GaAs compositionally graded quantum wells

Graded In _y Ga_{1 ? y} As quantum well epitaxial technology is developed for engineering the band potential profile. The crystal structure of the samples is clarified by high-resolution X-ray diffraction. The influence of quantum-well bending on the crystal and electron transport properties is studied on one- and two-side δ-doped Al_0.23Ga_0.77As/In _y Ga_{1 ? y} As/Al_0.23Ga_0.77As PHEMT heterostructures. The highest InAs content gradient reached is 1.2%/nm for the mean InAs content y = 0. 2. Optimization of the InAs content grading leads to an increase in the electron mobility and concentration. This effect is related to the straightening and deepening of the quantum-well potential profile. In addition, the electron wavefunction shifts toward the quantum-well center, thus reducing electron scattering.     

Electron transport in an In<Subscript>0.52</Subscript>Al<Subscript>0.48</Subscript>As/In<Subscript>0.53</Subscript>Ga<Subscript>0.47</Subscript>As/In<Subscript>0.52</Subscript>Al<Subscript>0.48</Subscript>As quantum well with a δ-Si doped barrier in high electric fields

The electron conduction in a two-dimensional channel of an In_0.52Al_0.48As/In_0.53Ga_0.47As/In_0.52Al_0.48As quantum well (QW) with a δ-Si doped barrier has been investigated. It is shown that the introduction of thin InAs barriers into the QW reduces the electron scattering rate from the polar optical and interface phonons localized in the QW and increases the electron mobility. It is found experimentally that the saturation of the conduction current in the In_0.53Ga_0.47As channel in strong electric fields is determined by not only the sublinear field dependence of the electron drift velocity, but also by the decrease in the electron concentration n _s with an increase in the voltage across the channel. The dependence of n _s on the applied voltage is due to the ionized-donor layer located within the δ-Si doped In_0.52Al_0.48As barrier and oriented parallel to the In_0.53Ga_0.47As QW.     

Characterization of GaAs/ InxGa1−x As quantum-dot heterostructures by electrical and optical methods

Results of electrical and optical studies of GaAs/In_xGa_1−x As heterostructures are reported. The aim of these studies was to identify the quantum dots and develop a technology of their growth by spontaneous transformation of an In_xGa_1−x As layer. The surface charge at the depth of the quantum dots and their surface density as a function of the deposition time of this narrow-band material are estimated by C-V profiling. A photoluminescence study of the quantum dots revealed peculiarities of the filling of their electron states at various excitation levels. The influence of Coulomb interactions on the optical properties of the quantum dots is discussed. Fiz. Tekh. Poluprovodn. 32, 111–116 (January 1998)     

Application of photoluminescence spectroscopy to studies of In0.38Al0.62As/In0.38Ga0.62As/GaAs metamorphic nanoheterostructures

The results of studies of the surface morphology, electrical parameters, and photoluminescence properties of In_0.38Al_0.62As/In_0.38Ga_0.62As/In_0.38Al_0.62As metamorphic nanoheterostructures on GaAs substrates are reported. Some micron-sized defects oriented along the [011] and \([0\bar 11]\) directions and corresponding to regions of outcropping of stacking faults are detected on the surface of some heterostructures. The Hall mobility and optical properties of the samples correlate with the surface defect density. In the photoluminescence spectra, four emission bands corresponding to the recombination of charge carriers in the InGaAs quantum well (1–1.2 eV), the InAlAs metamorphic buffer (1.8–1.9 eV), the GaAs/AlGaAs superlattice at the buffer-substrate interface, and the GaAs substrate are detected. On the basis of experimentally recorded spectra and self-consistent calculations of the band diagram of the structures, the compositions of the alloy constituents of the heterostructures are established and the technological variations in the compositions in the series of samples are determined.     

Galvanomagnetic properties of two-dimensional electron gases in strain relaxed InxGa1−xAs(x<0.40) heterostructures grown by molecular beam epitaxy on GaAs substrates

We have investigated, as a function of indium content x, the galvanomagnetic and Shubnikov de Haas (SdH) properties of two-dimensional electron gases (2DEG) formed at lattice matched, strain relaxed InAlAs/InGaAs heterojunctions. These were grown by molecular beam epitaxy on GaAs misoriented substrates with a two degree offcut toward the nearest (110) plane. Variable temperature resistivity and Hall measurements indicate an increase in the electron sheet density n_s from 0.78×10¹²cm⁻² for x=0.15 to 1.80×10¹² cm⁻² for x=0.40 at 300K, and from 0.75×10¹²cm⁻² to 1.67×10¹²cm⁻² at T=1.6K. The room temperature electron mobility, measured along the in plane [110], direction is independent of indium content and equals approximately 9500 cm²/Vs. For T<50K, the mobility is independent of temperature decreasing with increasing x from 82000 cm²/Vs for x=0.15 to 33000 cm²/Vs for x=0.40. The ratios (τ_t/τ_q) at 1.6K between the electron relaxation time τ_t and the single particle relaxation time τq, for the strain relaxed specimens, as well as for pseudomorphically strained Al_0.35Ga_0.65As/In_0.15Ga_0.85As structures grown on GaAs substrates, and In_0.52Al_0.48As/In_0.53Ga_0.47As heterostructures grown lattice matched on InP substrates. Such a study indicates the presence of inhomogeneities in the 2DEGs of the strain relaxed specimens which appear to be related to the process of strain relaxation. Such inhomogeneities, however, have little effect on the electron relaxation time τ_t which, at low temperatures, is limited principally by alloy scattering.     

Admittance spectroscopy of ring diode InGaAs/InAlAs/InP quantum-well structures

The admittance of ring planar diode Au/InGaAs/InP and Au/InGaAs/InAlAs heteronanostructures on i-InP has been studied. The structures are constituted by a silicon ??-doped layer and an InGaAs quantum well (QW) in InP or InAlAs epitaxial layers. An analysis of the capacitance-voltage and conductance-voltage characteristics yielded distribution profiles of the electron concentration and mobility in the vicinity of the QW and ??-doped layer. It is shown that lowering the temperature leads to an increase in the electron concentration and mobility in the QW.     

Photoluminescence studies of In0.7Al0.3As/In0.75Ga0.25As/In0.7Al0.3As metamorphic heterostructures on GaAs substrates

The influence of the design of the metamorphic buffer of In_0.7Al_0.3As/In_0.75Ga_0.25As metamorphic nanoheterostructures for high-electron-mobility transistors (HEMTs) on their electrical parameters and photoluminescence properties is studied experimentally. The heterostructures are grown by molecular-beam epitaxy on GaAs (100) substrates with linear or step-graded In _x Al_{1 ? x} As metamorphic buffers. For the samples with a linear metamorphic buffer, strain-compensated superlattices or inverse steps are incorporated into the buffer. At photon energies ?ω in the range 0.6–0.8 eV, the photoluminescence spectra of all of the samples are identical and correspond to transitions from the first and second electron subbands to the heavy-hole band in the In_0.75Ga_0.25As/In_0.7Al_0.3As quantum well. It is found that the full width at half-maximum of the corresponding peak is proportional to the two-dimensional electron concentration and the luminescence intensity increases with increasing Hall mobility in the heterostructures. At photon energies ?ω in the range 0.8–1.3 eV corresponding to the recombination of charge carriers in the InAlAs barrier region, some features are observed in the photoluminescence spectra. These features are due to the difference between the indium profiles in the smoothing and lower barrier layers of the samples. In turn, the difference arises from the different designs of the metamorphic buffer.     

Surface wave excitation auger electron spectroscopy of lnGaAs/GaAs(001) grown by alternate molecular-beam epitaxy

An angle-resolved electron-beam-excitation Auger-electron-spectroscopy, called as “surface wave excitation Auger electron spectroscopy (SWEAES),” was developed to characterize the semiconductor surface on an atomic scale. SWEAES enables us to get information about (1) surface valence electron states, (2) surface inner potentials concerned with high energy electron diffraction at the surface wave resonance (SWR) condition, (3) surface composition of ultra-thin heterostructures, and (4) confinement effects of diffracted surface electron waves at the SWR condition. These effects were demonstrated for In_1-x Ga _x As/GaAs(001)-c(8 × 2)-In/Ga and (GaAs)₂/(InAs)₁/GaAs(001) strained single quantum well surfaces. The current address: Dept. Elect. Eng., Faculty of Engineering, Kobe University, 1-1 Rokkodai-cho, Nada-Ku, Kobe, 657, JAPAN     

120nm栅长In0.7Ga0.3As/In0.52Al0.48As HEMTs 器件

利用新型的PMMA/PMGI/ZEP520/PMGI四层胶T形栅电子束光刻技术制备出120nm栅长InP基雁配In0.7Ga0.3As/In0.52Al0.48As 高电子迁移率晶体管。制作出的InP基HEMT器件获得了良好的直流和高频性能,跨导、饱和漏电流密度、阈值电压、电流增益截止频率和最大单向功率增益频率分别达到520 mS/mm, 446 mA/mm, -1.0 V, 141 GHz 及 120 GHz。文中的材料结构和所有器件制备均为本研究小组自主研究开发。     

Hooge parameter of InGaAs bulk material and InGaAs 2DEG quantum well structures based on InP substrates

The 1/f noise of various InGaAs layers lattice matched to InP is investigated systematically at room temperature. To elucidate the origin of the 1/f noise in this type of III–V compound semiconductor, thick n-type doped InGaAs layers, typical InP based InAlAs/InGaAs or InP/InGaAs heterostrucuture field-effect transistor (HFET) structures, respectively, as well as InP based InAlAs/InGaAs quantum well structures with doped InGaAs two-dimensional electron gas (2DEG) channel are analysed. From the experiments it is found that mobility fluctuation is the only origin for the 1/f noise observed both in InGaAs bulk material and in 2DEG heterostructures of high quality. A Hooge parameter attributed to phonon scattering α_Hphon in the bulk material is found to be about 7×10⁻⁶ and agrees with those obtained from HFET structures with the highest mobilities (α_H≈1.5×10⁻⁵). Furthermore, the Hooge parameter of 2DEG structures strongly depends on the channel design and on the doping concentration in the n-type doped 2DEG channels.     

Hall and photoluminescence studies of effects of the thickness of an additional In0.3Ga0.7As layer in the center of In0.15Ga0.85As/Al0.25Ga0.75As/GaAs high electron mobility transistors

In order to reduce the noise and carrier–donor scattering and thereby increase the carrier mobility of the pseudomorphic AlGaAs/InGaAs high electron mobility transistors (pHEMTs), we have grown Al_0.25Ga_0.75As/In_0.15Ga_0.85As/In_0.3Ga_0.7As/GaAs pHEMTs with varied In_0.3Ga_0.7As thickness, and studied the effects of the In_0.3Ga_0.7As thickness on the electron mobility and sheet density by Hall measurements and photoluminescence measurements. We calculated the electron and hole subbands and obtained good agreement between calculated and measured PL energies. It was found that the additional In_0.3Ga_0.7As layer could be used to reduce the carrier–donor scattering, but due to the increased interface roughness as the In_0.3Ga_0.7As layer becomes thicker, the interface scattering reduced the electron mobility. An optimal thickness of the In_0.3Ga_0.7As was found to be 2 nm.