InAlAs Layers Research Articles

Strain relaxation and surface morphology of high indium content InAlAs metamorphic buffers with reverse step

Low-temperature step-graded high indium content InAlAs (In% = 0.75) metamorphic buffer layers with reverse step layer grown on GaAs substrate by molecular beam epitaxy are investigated in this paper. The composition and the strain relaxation of the top InAlAs layer are determined by high-resolution triple-axis X-ray diffraction measurements, which show that the top InAlAs layer is nearly fully relaxed and the growth parameters for these samples have little influence on the strain relaxation ratio. Surface morphology is observed by reflection high-energy electron diffraction pattern and atomic force microscopy. The surface morphology is found to depend strongly on both the growth temperature and the As flux. Compared with other samples, the sample growth under the optimized conditions has the smallest value of root mean square surface roughness. Furthermore, the ω − 2 θ and ω scans of the triple-axis X-ray diffraction and transmission electron microscopy result also show the sample grown under the optimized conditions has good crystalline quality.

Highly selective and low damage atomic layer etching of InP∕InAlAs heterostructures for high electron mobility transistor fabrication

Highly selective, low damage atomic layer etching (ALET) technology was developed for dry gate recess during the fabrication of InGaAs∕InP∕InAlAs high electron mobility transistors lattice matched to InP substrates. Etching characteristics of InP layer on top of InAlAs layer and the surface chemistry of the exposed InAlAs layer were investigated by utilizing angular resolved x-ray photoelectron spectroscopy. Finally, InAlAs Schottky diodes were fabricated by utilizing chlorine-based ALET technology and conventional Ar-based dry recess and their electrical characteristics were compared. By using the ALET, the etch selectivity as high as 70:1 was achieved for InP over InAlAs heterostructures and the stoichiometric modification of InAlAs was observed to be negligible after the recess etch process. Schottky diodes fabricated after the ALET exhibited the lower ideality factor and the higher Schottky barrier height compared to those fabricated with Ar-based plasma etching.

HIGH TEMPERATURE STABILITY OF OPTICAL PROPERTIES OF InAs QUANTUM DOTS REALIZED BY CONTROLLING OF QUANTUM DOTS ELECTRONIC SPECTRUM

The optical properties of InAs /( Al ) GaAs quantum dots (QDs) overgrowth by thin AlAs / InAlAs layers are studied as a function of temperature from 10 to 500 K. The QDs emit at 1.27 μm at room temperature. It is shown that the QD energetic spectrum can be tuned by overgrowth of AlAs / InAlAs to provide high temperature stability of the QDs optical properties. Transport of carriers between neighboring QDs is absent, and the carrier distribution remains nonthermal up to room temperature. It is shown that suppression of the thermal escaping of the carriers from QDs is conditioned by high energy separation between ground and excited states, absence of wetting layer level, and increase of carrier localization energy in QDs in case of the Al 0.3 Ga 0.7 As matrix.

Improvement of Impact Ionization Effect and Subthreshold Current in InAlAs/InGaAs Metal–Oxide–Semiconductor Metamorphic HEMT With a Liquid-Phase Oxidized InAlAs as Gate Insulator

The oxidation of InAlAs and its application to InAlAs/InGaAs metal-oxide-semiconductor metamorphic high-electron mobility transistors (MOS-MHEMTs) are demonstrated in this study. After the highly selective gate recessing of InGaAs/InAlAs using citric buffer etchant, the gate dielectric is obtained directly by oxidizing the InAlAs layer in a liquid-phase solution at near room temperature. As compared to its counterpart MHEMT, the fabricated InAlAs/InGaAs MOS-MHEMT exhibits a larger tolerance to gate bias, higher breakdown voltage, lower subthreshold current, improved gate leakage current with the effectively suppressed impact ionization effect, and improved radio-frequency performance. Consequently, the liquid-phase oxidation may also be used to produce gate oxides and as an effective passivation on III-V compound semiconductor devices

Promising new valved source for Ga or In evaporation

A new valved source for evaporation of Ga or In has been demonstrated. Its performance in terms of controlling the group III flux has been shown to be very good to excellent in terms of response time (2–3s), reproducibility (∼1%), stability (∼0.1%), and shut-off ratio (at least 30:1). In addition, this cell has produced GaAs, InGaAs, and InAlAs layers with material quality comparable to other state-of-the-art sources in terms of uniformity, surface morphology, background doping, carrier mobility, and p-i-n device performance. Finally, it has been demonstrated that the graphite-based material used for the crucible and valve in this source does not generate any extra carbon doping compared to the usual pyrolytic boron nitride-based crucibles.

High performance InP/InAlAs/GaAsSb/InP double heterojunction bipolar transistors

DC and RF characteristics of InP/InAlAs/GaAsSb/InP double heterojunction bipolar transistors (DHBTs) are reported. The device heterostructures include InAlAs spacer layer between InP emitter and GaAsSb base layer. The impact of thin InAlAs spacer layer was investigated by comparing the DC characteristics of large-area devices fabricated on InP/InAlAs/GaAsSb/InP and conventional InP/GaAsSb/InP heterostructures. By suppressing the base tunneling current and surface recombination current, the DHBTs with thin InAlAs spacer layer exhibited 5 decade lower crossover current of 7 × 10 −11 A (collector current at unity current gain) than conventional InP/GaAsSb/InP DHBT that exhibited crossover current of 4 × 10 −6 A. The current gain also improved twice by the impact of thin InAlAs layer. To investigate the high-frequency characteristics of InP/InAlAs/GaAsSb/InP DHBTs, small-area devices employing laterally etched undercut micro-airbridges were fabricated. The unity current gain cut-off frequency, f T, of 100 GHz was obtained from a 1 × 30 μm 2 emitter DHBT.

Comparative study of GaAs‐based 1.5 micron‐range InAs/InGaAs and InAs/InAlAs self‐assembled quantum dots

AbstractOptical properties of self‐organized QDs grown on thick metamorphic InGaAs layers with different In composition are studied. The dots are formed by an overgrowth of original InAs islands with thin InGaAs or InAlAs layers. Room temperature photoluminescence at 1.55 µm is demonstrated for the sample with 27% In composition in the matrix. The overgrowth with InAlAs layers permits to eliminate the wetting layer states and increase energy separation between QD ground and excited states. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Low temperature step-graded InAlAs/GaAs metamorphic buffer layers grown by molecular beam epitaxy

Low-temperature step-graded InAlAs metamorphic buffer layers on GaAs substrate grown by molecular beam epitaxy were investigated. The strain relaxation and the composition of the top InAlAs layer were determined by high-resolution triple-axis x-ray diffraction measurements, which show that the top InAlAs layer is nearly fully relaxed. Surface morphology was observed by reflection high-energy electron diffraction pattern and atomic force microscopy. Under a selected range of growth parameters, the root mean square surface roughness of the sample grown at 380 °C is 0.802 nm, which has the smallest value compared with those of other samples.Furthmore, The ω-2θ and ω scans of the triple-axis x-ray diffraction, and photoluminescence show the sample grown at 380 °C has better crystalline quality. With decreasing As overpressure at this growth temperature, crystalline quality became poor and could not maintain two dimensional growth with increasing overpressure. The carrier concentrations and Hall mobilities of the InAlAs/ InGaAs/GaAs MM-HEMT structure on low-temperature step-graded InAlAs metamorphic buffer layers grown in optimized conditions are high enough to make devices.

Effect of incorporating an InAlAs layer on electron emission in self-assembled InAs quantum dots

We perform capacitance-voltage and admittance spectroscopy to investigate the effect of incorporating an InAlAs layer before an InGaAs cap layer on electron emission in self-assembled InAs quantum dots (QDs). We show that this incorporation of a high potential barrier increases the emission time of the electrons thermally activated from the QD ground to the first excited state. The energy separation between the ground and first excited states in the conduction band increases from 57.2 to 79.1, to 89.2, and to 95.6 meV with increasing the thickness of the InAlAs layer from 0 to 10, to 14, and to 20 Å. Combining with photoluminescence (PL) data, the ratios of the energy separation between the ground and first excited states in the conduction band and valence band are determined to be 7.3:2.7 and 7.8:2.2 for 0 and 10 Å InAlAs, respectively. In addition, this incorporation is shown to blueshift the PL first excited state much larger than the ground state.

Suppression of surface segregation of silicon dopants during molecular beam epitaxy of (411)A In[sub 0.75]Ga[sub 0.25]As∕In[sub 0.52]Al[sub 0.48]As pseudomorphic high electron mobility transistor structures

The authors achieved considerable suppression of surface segregation of Si dopants in In0.75Ga0.25As∕In0.52Al0.48As high electron mobility transistor (HEMT) structures grown on (411)A InP substrates by molecular beam epitaxy (MBE). The (411)A HEMT structures were conventionally grown at a high substrate temperature (Ts) of 540°C in order to form the extremely flat (411)A heterointerfaces. This results in considerable surface segregation of Si dopants. Surface segregation of Si dopants was suppressed by lowering growth temperature of the top InAlAs barrier layer (TB) down to 450°C with keeping Ts of 540°C for other parts. Sheet carrier concentration (Ns) of two-dimensional electron gas (2DEG) was measured as a function of thickness (Lb) of the top InAlAs barrier for TB=450 and 540°C samples. Observed Ns of the TB=540°C sample vanished when Lb approached to 7nm, while 2DEG with of Ns∼2×1012cm−2 remained for the TB=450°C sample. Surface segregation of Si-sheet-doped (411)A InAlAs layers grown at TB was also ...

Optical properties of self-assembled InAs/InAlAs/InP quantum wires with different InAs deposited thickness

We report on the photoluminescence (PL) properties of InAs/InAlAs/InP quantum wires (QWRs) with various InAs deposited thickness. The PL linewidth of the QWRs decreases with increasing InAs deposited thickness due to the different thicknesses of the QWRs and defects in the samples. The defects and lateral composition modulation of the InAlAs layers play an important role in the temperature-dependent PL properties of the samples.

Self-organized superlattices along the [001] growth direction in In 0.52Al 0.48As layers grown on nominally (001) InP substrates by molecular beam epitaxy

Horizontal self-organized superlattice structures consisting of alternating In-rich and Al-rich layers formed naturally during solid-source molecular beam epitaxy (MBE) growth of In 0.52Al 0.48As on exactly (001) InP substrates, with In and Al fluxes unchanged. The growth temperatures were changed from 490 to 510 ∘C, the most commonly used growth temperature for In 0.52Al 0.48As alloy. No self-organized superlattices (SLs) were observed at the growth temperature 490 ∘C, and self-organized SLs were observed in InAlAs layers at growth temperatures ranging from 498 to 510 ∘C. The results show that the period of the SLs is very highly regular, with the value of ∼6 nm, and the composition of In or Al varies approximately sinusoidally along the [001] growth direction. The theoretical simulation results confirm that the In composition modulation amplitude is less than 0.02 relative the In composition of the In 0.52Al 0.48As lattice matched with the InP substrate. The influence of InAs self-organized quantum wires on the spontaneously formed In x Al 1− x As/In y Al 1− y As SLs was also studied and the formation of self-organized In x Al 1− x As/In y Al 1− y As SLs was attributed to the strain-mediated surface segregation process during MBE growth of In 0.52Al 0.48As alloy.

Carrier dynamics in Ga0.53In0.47As∕InP near-surface quantum wells

Ga 0.53 In 0.47 As ∕ InP single-quantum wells with thin top barrier layers of InP and InAlAs have been studied by pump-probe experiments and temperature-dependent photoluminescence spectroscopy. The carrier lifetimes are shorter in samples with an InAlAs surface barrier than with an InP surface barrier. The decays consist in an early stage decay of typically 30 ps and an extended stage decay of several hundreds of picoseconds. This nonexponential relaxation is the result of thermally activated carrier escape, trapping, and recombination on the surface states. Two nonradiative surface states, at 11 and 68 meV from the ground state of the quantum well, were identified.

Growth of InP high electron mobility transistor structures with Te doping

InP high electron mobility transistor (HEMT) structures with In 0.53Ga 0.47As channels and In 0.52Al 0.48As barriers were grown by molecular beam epitaxy. A GaTe source was used as an n-type dopant. Conventional structures with 50–100 Å InAlAs(Te) layers and Te-delta-doped structures were investigated. Both types of structures exhibited good transport characteristics, with mobilities of 8000–10,000 cm 2/V-s and sheet densities of 1–4×10 12/cm 2. Fluorination studies showed similar behavior for Si- and Te-doped HEMT structures, with donor deactivation resulting in substantial reductions in mobility and carrier density after exposure to fluorine.

A Novel Two-Color Photodetector Based on an InAlAs–InGaAs HEMT Layer Structure

The spectral responsivity of an InAlAs-InGaAs metal-semiconductor-metal diode above a two-dimensional electron gas (2DEG) is investigated as a function of the applied bias. At low voltages, only the InAlAs layer above the 2DEG contributes to the photocurrent, while the InGaAs channel layer is activated at higher bias. This results in a voltage-dependent spectral response of the photodetector. The ratio of the responsivities at 1300 and 850 nm changes from 0.03- at 1-V to 0.44- at 1.6-V bias. This property makes the device a candidate suitable to detect and to separate optical information originated both from the GaAs (850 nm) and in the InGaAs (1300, 1550 nm)-based optoelectronic technology.

Strong charge carrier confinement in purely strain induced GaAs∕InAlAs single quantum wires

We report on micro-photoluminescence studies of single quantum wires which were grown by molecular beam epitaxy. Employing the cleaved edge overgrowth technique, quantum wires located in an overgrown (011) oriented GaAs quantum well originate purely from the tensile strain field of InAlAs layers grown along the [100] direction. These stressor layers are separated by 1-μm-wide AlGaAs barriers so that the photoluminescence signals of different quantum wires can be resolved individually. Their confinement energy varies systematically with the widths of the stressor and overgrown layers, reaching values as high as 51.5meV. The quantum wire signals are characterized by a smooth line shape even for the lowest excitation powers, indicating the absence of pronounced exciton localization.

Growth of nanostructures on composition-modulated InAlAs surfaces

InAs self-organized nanostructures were grown with variant deposition thickness andgrowth rate on closely matched InAlAs/InP by molecular-beam epitaxy. Thestructural properties of InAs and InAlAs layer were studied. It is found that theInAs morphology is insensitive to the growth conditions. Transmission electronmicroscopy and reflectance difference spectroscopy measurements show that theInAlAs matrix presents lateral composition modulation which gives birth to surfaceanisotropy. Based on the dependence of the InAs morphology on the anisotropy ofthe InAlAs layer, a modified Stranski–Krastanow growth mode is presented todescribe the growth of the nanostructure on a composition-modulated surface.

Electron g factor in a gated InGaAs channel with double InAs-inserted wells

We report the gate-voltage dependence of the electron g factor in InGaAs/InAlAs heterostructures with double InAs-inserted wells. The g factor has been determined from a series of Shubnikov–de Haas oscillations at various angles with respect to the layers under different gate voltages. The strain in InAs layers and the penetration of the electron wave function into InGaAs and InAlAs layers are the important factors of the reduction in the | g| factor. We have also observed the changes of the | g| factor with respect to the gate voltage, though this dependence is not clear in the simple calculation.

Photoluminescence of Self-Assembled InAs/GaAs Quantum DotsCovered by InAlAs and InGaAs Combination Strain-Reducing Layer

Self-assembled InAs/GaAs quantum dots covered by the 1-nmInxAl(1−x)As (x = 0.2,0.3) and 3-nmIn0.2Ga0.8As combination strain-reducing layer arefabricated, whose height can take up to 30–46 nm. The luminescenceemission at a long-wavelength of 1.33 μm and the energy separationbetween the ground and the first-excited state of 86 meV are observedat room temperature. Furthermore, comparative study proves that theenergy separation can increase to 91 meV by multiple stacking.

Engineering carrier confinement potentials in 1.3-μm InAs/GaAs quantum dots with InAlAs layers: Enhancement of the high-temperature photoluminescence intensity

We describe an optical study of structures consisting of an InAlAs-GaAs strained buffer layer and an InAlAs-InGaAs composite strain-reducing layer designed to modify the confining potential of 1.3-μm InAs/GaAs quantum dots (QDs). With increasing (decreasing) InAlAs (InGaAs) thickness in the strain-reducing layer grown above the QDs, the integrated photoluminescence (PL) intensity of the QD ground-state transition increases dramatically and the emission wavelength decreases slightly from 1.36 to 1.31 μm. The enhancement of PL efficiency is temperature dependent, being much greater above 200 K. A maximum enhancement of 450 is achieved at room temperature. This improvement of the high-temperature PL efficiency should lead to a significant improvement in the characteristics of 1.3-μm InAs/GaAs QD lasers.