Field dependence of mobility in Al0.2Ga0.8As/GaAs heterojunctions at very low fields

Multiple-period (Al, Ga)As/GaAs modulation doped heterojunction structures have been grown with molecular beam epitaxy. Electron mobilities of about 200 000 cm2/Vs at 10 K and 90000 cm2/Vs at 77 K with associated sheet carrier concentrations of about 2×1012 cm?2 have been observed. The current parallel to the interfaces for low electric fields was examined as a function of lattice temperature. The electron mobility has been observed to be strongly dependent on the strength of the electric field, and hot electron effects were observable at a field as low as 10 V/cm. To our knowledge this is the first report of hot electron phenomena in GaAs at such small fields.     

High-mobility selectively doped GaAs/GaAlAs structures grown by low-pressure OM-VPE

We report the growth of high-quality selectively doped GaAs/GaAlAs heterostructures grown by OM-VPE. Electron mobilities as high as 162000 cm2V?1s?1 have been obtained at 2 K. The sheet carrier concentration was varied between 5 × 1011 cm?2 and 1.5 × 1012 cm?2 by changing the `spacer? thickness and the doping level in the n-type GaAlAs.     

Three period (Al,Ga)As/GaAs heterostructures with extremely high mobilities

Selectively doped three period Al0.2Ga0.8As/GaAs structures have been grown by molecular beam epitaxy and characterised by Hall effect over a temperature range of 10 K?300 K. Electron mobilities as high as 211 000, 95 800 and 6700 cm2V?1s?1 have been obtained at 10 K, 78 K and 300 K, respectively. The total charge concentration in all the structures was about 2.25×1012 cm?2. These extremely high electron mobilities are a result of separating the donors and the electrons appreciably, and very-high-quality interfaces. To date, the figures at 78 K are the highest reported, while the 10 K figures are about twice the best previously reported results.     

Sheet electron concentration at the heterointerface in Al0.48In0.52As/Ga0.47In0.53As modulation-doped structures

Sheet electron concentration at the heterointerface in Al0.48In0.52As/Ga0.47In0.53As modulation-doped structures has been calculated as a function of the spacer layer thickness, the doping concentration in Al0.48In0.52As and the lattice temperature. The calculated results were compared with those for Al0.3Ga0.7As/GaAs structures and also with the experimental data. It is shown that, compared with AlGaAs/GaAs about 1.5 times higher sheet electron concentration can be obtained in AlInAs/GaInAs at the same doping level, which is in good agreement with the experimental results.     

In0.53Ga0.47As liquid phase epitaxy on (100)-InP substrates at low growth temperatures

In0.53Ga0.47As epitaxial layers of high quality and excellent surface morphology have been grown in an automated LPE system. The growth temperature was varied between 500 and 63O°C. Room-temperature Hall measurements indicated a net carrier concentration of n = 8 × 1014 cm?3 and mobility values of ? = 13000 cm2V?1 s?1 at TG 617°C and n = 7.7 × 1015 cm?3 and ? = 9800 cm2 V?1 s?1 at TG = 517°C, respectively.     

Room-temperature operation of Ga0.47In0.53As/AI0.48In0.52As resonant tunnelling diodes

The first room-temperature operation of Ga0.47In0.53As/Al0.48In0.52As resonant tunnelling (RT) diodes is reported. The peak/valley ratio of the current is as high as 4:1 at room temperature and is 15:1 at 80 K. These are the highest values of peak/valley ratio at the respective temperatures, reported so far, in this material system. The position of the peak in the current/voltage characteristic also showed good agreement with that obtained from an electron tunnelling transmission calculation.     

Enhancement of electron velocity in modulation-doped (Al,Ga)As/GaAs FETs at cryogenic temperatures

High-performance normally-off modulation-doped (Al,Ga)As/GaAs field-effect transistors with a 1 ?m gate length were fabricated and characterised. The transconductance obtained was 225 mS/mm at 300 K and 400 mS/mm at 77 K, leading to intrinsic transconductances (zero source resistance) of 305 and 565 mS/mm at 300 and 77 K, respectively. Since the device performance in short-gate transistors is limited by the electron saturation velocity, the increasing transconductance observed as the device is cooled is due to an increase in the electron velocity from about 2×107 cm/s to 3×107 cm/s. These velocities are inferred from a model developed for modulation-doped transistors and are predicted by pulse measurements in similar structures.     

Mn as a p-type dopant in In0.53Ga0.47As on InP substrates

Mn has been used as a p-type dopant in LPE In0.53Ga0.47As. The distribution coefficient was measured as 0.6 and the activation energy was 52.5±2.5 meV. The room temperature mobility varied from 183 to 94 cm2 V?1s?1 in the concentration range studied. A solid to solid diffusion coefficient of 2.6×10?12 cm2 s?1 was estimated for Mn into the substrate at 640°C.     

Enhanced mobility in inverted AlxGa1?xAs/GaAs heterojunctions: binary on top of ternary

Single-period modulation doped inverted Al0.18Ga0.82As/GaAs heterostructures having the binary on top of the ternary were grown by molecular beam epitaxy. Despite the early reports of no mobility enhancement, considerable mobility enhancement, particularly at cryogenic temperatures, were obtained in the present structures. Mobilities of about 27 600 cm2/Vs with associated sheet carrier concentrations of about 6×1011 cm?2 were obtained at 10 K. The results represent the first enhanced mobilities obtained by molecular beam epitaxy and compare with 25 600 cm2/Vs deduced from Shubnikov de Haas measurements in LPE-grown structures at 4 K.     

High-mobility Ga0.47In0.53As thin epitaxial layers grown by MBE, very closely lattice-matched to InP

Thin epitaxial layers (< 1.5 ?m) of Ga0.47In0.53As were grown by molecular beam epitaxy, very closely lattice-matched to InP, despite a nonrotating substrate holder. Hall mobilities were measured as a function of temperature in the dark and on illumination. At low temperature, the peak mobility of undoped layers lies between 35000 and 40000 cm2V?1s?1 in the dark and increases up to 45000 cm2V?1s?1 when measured in the light. Preliminary results obtained on slightly Sn-doped layers are also reported.     

Quantum-well-doped FET (QUD-FET)

A novel FET using a 2DEG is presented. The FET has an AlAs/GaAs/AlAs single quantum well with planar doping in the centre of the GaAs layer. The conduction channels are composed of a 2DEG generated in undoped GaAs layers outside the well. The measured 2DEG concentration was 1.8?2 × 1012cm?2 with electron mobilities of 3500cm2/Vs at RT and 10500cm2/Vs at 77K. A 1.5?m-gate-length FET exhibits a maximum transconductance of 174 mS/mm and a maximum current exceeding 300 mA/mm at 77K.     

Growth of Ga0.47In0.53As on InP by low-pressure m.o. c.v.d.

The first heteroepitaxy is reported of Ga0.47In0.53As on InP by low-pressure metalorganic chemical vapour deposition (m.o. c.v.d.). Triethylindium (t.e.i.) and triethylgallium (t.e.g) were used as group III sources, and arsine as the group V source. These Ga0.47In0.53As epilayers exhibit high electron mobility (7.74 cm2 V?1 s?1 for a total impurity concentration of 2.5 × 1016 cm?3 at 300 K) and a photoluminescence efficiency comparable to l.p.e. layers. The lattice mismatch is only ?a0/a0 ? 4 × 10?4. Our mobility measurements indicate that m.o. c.v.d. Ga0.47In0.53As is a promising material for microwave device applications.     

Novel multilayer modulation doped (Al,Ga)As/GaAs structures for self-aligned gate FETs

The fabrication of self-aligned gate by ion implantation modulation doped (Al,Ga)As/GaAs field effect transistors (MODFETs) utilising a novel multilayer structure capable of withstanding the high-temperature furnace anneals required for Si implant activation is reported. Typical measured extrinsic transconductances of 175 mS/mm at 300 K and 290 mS/mm at 77 K were achieved on 1.1 ?m-gate-length devices. Values of the two-dimensional electron gas saturation velocity of 1.9×107 cm/s at 300 K and 2.7×107 cm/s at 77 K were obtained from an analysis of the FET drain current/voltage characteristics using the charge-control model.     

Persistent photoconductivity and electron mobility in In0.52Al0.48As/In0.53Ga0.47As/In0.52Al0.48As/InP quantum-well structures

The influence of the width of the quantum well L and doping on the band structure, scattering, and electron mobility in nanoheterostructures with an isomorphic In_0.52Al_0.48As/In_0.53Ga_0.47As/In_0.52Al_0.48As quantum well grown on an InP substrate are investigated. The quantum and transport mobilities of electrons in the dimensionally quantized subbands are determined using Shubnikov-de Haas effect measurements. These mobilities are also calculated for the case of ionized-impurity scattering taking into account intersub-band electron transitions. It is shown that ionized-impurity scattering is the dominant mechanism of electron scattering. At temperatures T < 170 K, persistent photoconductivity is observed, which is explained by the spatial separation of photoexcited charge carriers.     

Effects of growth temperature and [PH3]/[In(C2H5)3] on purity of epitaxial InP grown by metalorganic chemical vapour deposition

High-purity undoped InP epitaxial layers (ND ? NA = 5 × 1014 cm?3, ?77?105 cm2/Vs) are grown by low-pressure metalorganic chemical vapour deposition. The carrier concentrations decrease and the electron mobilities increase as the growth temperature decreases from 700°C to 575°C and the mole fraction ratios ([PH3]/[In(C2H5)3]) increase from 29 to 290.     

InP基功率HEMT结构材料分子束外延生长研究

从 3个层面研究了分子束外延 Al0 .48In0 .52 As/ Ga0 .47In0 .53As/ In P功率 HEMT结构材料生长技术。首先 ,通过观察生长过程的高能电子衍射 (RHEED)图谱 ,确立了 Ga0 .47In0 .53As/ In P结构表面层的 MBE RHEED衍射工艺相图 ,据此生长的单层 Si-doped Ga0 .47In0 .53As(40 0 nm) / In P室温迁移率可达 6960 cm2 / V· s及电子浓度 1 .3 3 E1 7cm- 3。其次 ,经过优化结构参数 ,低噪声 Al0 .48In0 .52 As/ Ga0 .47In0 .53As/ In P HEMT结构材料的 Hall参数达到μ30 0 K≥ 1 0 0 0 0 cm2 / V· s、2 DEG≥ 2 .5 E1 2 cm- 2 。最后 ,在此基础之上 ,降低 spacer的厚度、在 Ga0 .47In0 .53As沟道内插入 Si平面掺杂层并增加势垒层的掺杂浓度获得了功率 Al0 .48In0 .52 As/ Ga0 .47In0 .53As/ In PHEMT结构材料 ,其 Hall参数达到μ30 0 K≥ 80 0 0 cm2 / V· s、2 DEG≥ 4 .0 E1 2 cm- 2 。     

p-Channel (Al,Ga)As/GaAs modulation-doped logic gates

The operation of logic gates composed of modulation-doped field-effect transistors based on two-dimensional hole-gas conduction is reported for the first time. Direct coupled inverters fabricated on an MBE grown Be-doped (Al,Ga)As/GaAs wafer having a sheet density of 1.5 × 10¹²cm^-2and a 77K mobility of 1800 cm²/V.s exhibit logic states of -0.25 and -0.98 V at 77K for a - 1-V bias. Propagation delays of 233.0 ps/gate are obtained at 77K in ring-oscillator circuits with a power dissipation of 0.31 mW/gate. Power-delay products as low as 9.1 fJ are also obtained.     

In0.48Ga0.52P/In0.20Ga0.80As/GaAs pseudomorphic high electron mobility transistors grown by solid-source molecular-beam epitaxy using a valved phosphorus cracker cell

In_0.48Ga_0.52P/In_0.20Ga_0.80As/GaAs pseudomorphic high electron mobility transistor (p-HEMT) structures were grown by solid-source molecular beam epitaxy (SSMBE) using a valved phosphorus cracker cell. The sheet carrier density at room temperature was 3.3 × 10¹²cm^?2. A peak transconductance (G _m) of 267 mS mm^?1 and peak drain current density (I _ds) of 360 mA mm^?1 were measured for a p-HEMT device with 1.25 µm gate length. A high gate-drain breakdown voltage (BV _gd) of 33V was measured. This value is more than doubled compared with that of a conventional Al_0.30Ga_0.70As/In_0.20Ga_0.80As/GaAs device. The drain-source breakdown voltage (BV _ds) was 12.5V. Devices with a mushroom gate of 0.25 µm gate length and 80 µm gate width achieved a peak transconductance (G _m) of 420 mS mm^?1 and drain current density of nearly 500mA mm^?1. A high cutoff frequency (f _T) of 58GHz and maximum oscillation frequency (f _max) of 120 GHz were obtained. The results showed that the In_0.48Ga_0.52P/In_0.20Ga_0.80As/GaAs material system grown by SSMBE using the valved phosphorus cracker cell for the In^0.48Ga^0.52P Schottky and spacer layers is a viable technology for high frequency p-HEMT device applications.     

Schottky-barrier height of In0.43Al0.57As

The Schottky-barrier height of n-type In0 43Al0.57As grown by molecular-beam epitaxy on (100)-oriented n-type InP substrates measured by capacitance/voltage and internal photoemission measurements is ?Bn = 1.2 ± 0.1 eV, comparable to that of AlAs and substantially larger than that of In0.52Al0.48As.     

Effect of As4/Ga flux ratio on electrical properties of NID GaAs layers grown by MBE

The effect of the As4/Ga flux ratio R on NID GaAs layers has been studied when the MBE growth chamber is used without baking after reloading the arsenic cells, in order to increase the productivity of the system. In these conditions a change from p- to n-type is observed when R is varied from 1.8 to 14. Satisfactory p-type material is obtained at R ? 3 (p = 2.0 × 1014 cm?3, ?77 K = 6200 cm2 V?1 s?1). The maximum n-type mobility occurs at R = 5.8. Photoluminescence spectroscopy confirms the effect of R on the incorporation of residual impurities.