Lattice-mismatched GaAs Substrates Research Articles

Influence of GaAs and GaSb substrates on detection parameters of InAs/GaSb superlattice-based mid-infrared interband cascade photodetectors.

The paper presents electrical and optical properties of interband cascade infrared photodetectors with InAs/GaSb type-II superlattice absorbers. We compare the detection parameters of detectors grown on the native GaSb substrate and lattice-mismatched GaAs substrate and seek solutions to enhance device performance, specifically with using an optical immersion. The detectors grown on GaAs have better detection parameters at room temperature, but, at lower temperatures, the misfit dislocations become more important, and detectors grown on GaSb become better.

Mechanical Nano-Patterning: Toward Highly-Aligned Ge Self-Assembly on Low Lattice Mismatched GaAs Substrate

Low-dimensional semiconductor structurers formed on a substrate surface at pre-defined locations and with nano-precision placement is of vital interest. The potential of tailoring their electrical and optical properties will revolutionize the next generation of optoelectronic devices. Traditionally, highly aligned self-assembly of semiconductors relies on Stranski- Krastanov growth mode. In this work, we demonstrate a pathway towards ordered configuration of Ge islands on low lattice mismatch GaAs (110) substrate patterned using depth-controlled nanoindentation. Diamond probe tips with different geometries are used to nano-mechanically stamp the surface of GaAs (110). This creates nanoscale volumes of dislocation-mediated deformation which acts to bias nucleation. Results show that nanostamped GaAs exhibits selective-nucleation of Ge at the indent sites. Ge islands formed on a surface patterned using cube corner tip have height of ~10 nm and lateral size of ~225 nm. Larger islands are formed by using Vickers and Berkovich diamond tips (~400 nm). The strain state of the patterned structures is characterized by micro-Raman spectroscopy. A strain value up to 2% for all tip geometries has been obtained. Additionally, strong room temperature photoluminescence (PL) emission is observed around 1.9 µm (650 meV). The observed strain-induced enhancement in the light-emission efficiency is attributed to direct conduction to heavy-hole (cΓ-HH) and conduction to light-hole (cΓ-LH) transitions. The inherent simplicity of the proposed method offers an attractive technique to manufacture semiconductor quantum dot structures for future electronic and photonic applications.

Bandgap energy determination of InAsSb epilayers grown by molecular beam epitaxy on GaAs substrates

InAsSb ternary alloys can be considered as an alternative to HgCdTe for mid-wavelength, as well as long-wavelength infrared applications. Its energy bandgap exhibits nonlinearity versus Sb composition, and hence the correct determination of its value is necessary for the effective design and simulation of optoelectronic devices. The commonly used expression on the InAsSb energy bandgap provided by Wieder and Clawson overestimated energy bandgap values at high temperatures. In this paper, we present two modified empirical relationships which are based on the experimental data obtained in our laboratory and published literature. Both are correct for a wide range of Sb molar composition and temperatures.The nonlinearity of the energy gap is described with the adequate bowing parameter. The data collected in our experiment, for samples grown on lattice mismatched GaAs substrates, fits well with a bowing factor of C = 0.72 eV. The minimum bandgap energy that can be reached at room temperature is about 73 meV for a Sb mole fraction, x = 0.63. In comparison, the bandgap at low temperatures collected in the literature for samples grown on lattice-matched GaSb substrates is smaller than the measured values in our experiment and fits well with a parabola with C = 0.9 eV.

Performance evaluation of InAs/GaSb superlattice photodetector grown on GaAs substrate using AlSb interfacial misfit array

We report on the growth and opto-electronic characterization of type-II InAs/GaSb superlattice (SL) mid-wavelength infrared pin photodetector grown on a GaAs substrate. AlSb interfacial misfit array was employed at the GaAs buffer/GaSb epilayer interface to reduce the dislocation density of the SL structure grown on the lattice mismatched GaAs substrate. Optical and electrical performance of this sample (SL-GaAs) were then compared with the reference sample of the same structure grown on a GaSb substrate (SL-GaSb). At 80 K, the dark current density and the detectivity values of the pin photodetectors were recorded as 5.40 × 10−3 A cm−2 and 2.34 × 1010 cm Hz0.5 W−1 for the SL-GaAs and 9.50 × 10−4 A cm−2 and 4.70 × 1010 cm Hz0.5 W−1 for the SL-GaSb, respectively.

Mid-infrared metamorphic interband cascade photodetectors on GaAs substrates

Antimony-based mid-infrared interband cascade (IC) photodetectors fabricated on (001) GaAs substrates are reported. By using a “buffer-free” interfacial misfit array growth method, an overall good crystalline quality is obtained on the largely lattice-mismatched GaAs substrate. The GaAs-based IC detectors show comparable optical performance, with similar electrical performance at temperatures higher than 140 K, as compared to the reference devices grown on GaSb substrate. The GaAs-based IC detectors demonstrate dark current density of 2.63 × 10−6 A/cm2 at 180 K, which is about twice as compared to that grown on GaSb substrate, with Johnson-limited D* of 1.06 × 1011 Jones at 180 K and 4.0 μm. The results indicate that IC detector design is robust and relatively insensitive to the material quality, and metamorphic IC detector is viable for large-format infrared focal plane array applications.

Studies of scattering mechanisms in gate tunable InAs/(Al,Ga)Sb two dimensional electron gases

A study of scattering mechanisms in gate tunable two dimensional electron gases confined to InAs/(Al,Ga)Sb heterostructures with varying interface roughness and dislocation density is presented. By integrating an insulated gate structure the evolution of the low temperature electron mobility and single-particle lifetime was determined for a previously unexplored density regime, 1011–1012 cm−2, in this system. Existing theoretical models were used to analyze the density dependence of the electron mobility and single particle lifetime in InAs quantum wells. Scattering was found to be dominated by charged dislocations and interface roughness. It was demonstrated that the growth of InAs quantum wells on nearly lattice matched GaSb substrate results in fewer dislocations, lower interface roughness, and improved low temperature transport properties compared to growth on lattice mismatched GaAs substrates.

High-Resolution X-Ray Diffraction Studies on MBE-Grown p-ZnTe/n-CdTe Heterojunctions for Solar Cell Applications

High-resolution X-ray di ractometer was used to study structural quality, lattice parameters and mis t strain in p-ZnTe/n-CdTe heterojunctions grown by the molecular-beam epitaxy technique on two di erent (001)-oriented substrates of GaAs and CdTe. The X-ray di ractometer results indicate that the CdTe layers, grown on lattice mismatched GaAs substrate, are partially relaxed, by the formation of mis t dislocations at the interface, and display residual vertical strain of the order of 10−4. The presence of threading dislocations in the layers e ectively limits the e ciency of solar energy conversion in the investigated heterojunctions. Homoepitaxially grown CdTe layers, of much better structural quality, display unexpected compressive strain in the layers and the relaxed lattice parameter larger than that of the substrate. Possible reasons for the formation of that unusual strain are discussed.

Development of III-Sb Technology for p-Channel MOSFETs

Alternative channel materials with superior transport properties over conventional silicon based systems are required for supply voltage scaling in CMOS circuits. Group III- Sb 's are a candidate for high mobility p-channel applications due to a low hole effective mass, large injection velocity in scaled devices and the ability to achieve enhanced hole mobility in strained quantum wells (QW). Multiple challenges in antimonide MOSFET development are assessed and developed technologies were implemented into p-channel MOSFET fabrication with a low thermal processing budget of 350°C. These challenges include growth of “bulk” GaSb and bi-axial compressively strained In x Ga 1-x Sb QW channels on lattice mismatched GaAs substrates, reduction of interface trap state density (Dit) at the III- Sb /high-k oxide interface and avoiding ion implanted source and drain contacts with high temperature activation annealing. A “self-aligned” single mask p-channel MOSFET fabrication process was developed on buried In 0.36 Ga 0.64 Sb QW channels using intermetallic source and drain contacts. The first “gate-last” MOSFET process on In 0.36 Ga 0.64 Sb QW channels with pre-grown epitaxial p++- GaSb contacts is demonstrated. InAs has been proven to be an excellent etch stop layer when using an optimized tetramethylammonium hydroxide (TMAH) etch of p++- GaSb to prevent InGaSb QW damage.

Determination of the thickness and spectral dependence of the refractive index of Al x In1 − x Sb epitaxial layers from reflectance spectra

A nondestructive method for measuring the thicknesses of epitaxial layers of AlxIn1 − xSb alloys based on interference effects in reflectance spectra measured in a wide wavelength range (1–28 μm) is implemented. The studied 0.9–3.3 μm thick AlxIn1 − xSb layers are grown on highly lattice-mismatched GaAs substrates by molecular beam epitaxy. The found thicknesses are in good agreement with the independent data of scanning electron microscopy. The spectral dependence of the refractive index n(E) of AlxIn1 − xSb layers is measured both for the regions of transparency and fundamental absorption. The refractive index for the case of E E0 are found based on the interference pattern.

NBn dark current reduction by UV hydrogenation

This study reports on hydrogenation of InAs nBn photodetectors grown on a lattice mismatched GaAs substrate. The mismatched growth causes increases in dark current by factors of 8–16 (voltage- and temperature-dependent), with respect to similar lattice matched growth. UV hydrogenation of the mismatched nBn’s produced significant decrease in dark current without decreasing the photocurrent.

Capture kinetics at deep-level defects in MBE-grown CdTe layers

The results of deep-level transient spectroscopy (DLTS) investigations in n-type CdTe layers grown by the molecular-beam epitaxy (MBE) technique on lattice-mismatched GaAs substrates are described. Three electron traps and one hole trap, at rather low concentrations of the order of 1013 cm−3, have been revealed in the DLTS spectra measured under various bias conditions of Schottky diodes prepared on the as-grown CdTe layers. One of the electron traps has been attributed to electron states of dislocations on the ground of the logarithmic capture kinetics for capture of electrons into the trap states. The other three traps, displaying exponential capture kinetics, have been attributed to native point defects produced during the epitaxial growth of CdTe. The microscopic nature of the defects responsible for the traps is discussed taking into account recent results of first-principles calculations of the properties of dominant native defects in CdTe.

Properties of InSbN grown on GaAs by radio frequency nitrogen plasma-assisted molecular beam epitaxy

We report the growth of InSbN on a lattice-mismatched GaAs substrate using radio frequency nitrogen plasma-assisted molecular beam epitaxy. The effects of a two-step thin InSb buffer layer grown at 330 and 380 °C and substrate temperature (270–380 °C) on the properties of the InSbN are studied. The crystalline quality of the InSbN is significantly improved by the two-step buffer layer due to defect suppression. The shifting in the absorption edge of the InSbN from ∼5 to 8 µm following an increase in the substrate temperature is correlated with the reduction in free carrier concentration from ∼1018 to 1016 cm−3 and increase in concentration of N substituting Sb from ∼0.2 to 1%. These results will be beneficial to those working on the pseudo-monolithic integration of InSbN detectors on a GaAs platform.

Comparison of short period InAs/GaSb superlattices on GaSb and GaAs substrates

Type II superlattices (SLs) short period InAs(4ML)/GaSb(8ML) were grown by molecular-beam epitaxy on lattice-mismatched GaAs substrates and on GaSb substrates. A smooth GaSb epilayer was formed on GaAs substrates by inserting mulit-buffer layers including an interfacial misfit mode AlSb quantum dot layer and AlSb/GaSb superlattices smooth layer. SLs grown on GaAs substrates (GaAs-based SLs) showed well-resolved satellite peaks in XRD. GaSb-based SLs with better structural quality and smoother surface showed strong photoluminescence at 2.55 μm with a full width at half maximum (FWHM) of 20 meV, narrower than 31 meV of GaAs-based SLs. Inferior optical absorption of GaAs-based SL was observed in the range of 2–3 μm. Photoresponse of GaSb-based SLs showed the cut-off wavelength at 2.6 μm.

Growth mechanisms and crystallographic structure of InP nanowires on lattice-mismatched substrates

We present a growth model that predicts the growth phase and mechanism of InP nanowires (NWs) and the experimental verifications of the model. The NWs were grown on lattice-mismatched GaAs substrates using metal-organic chemical vapor deposition via Au nanodrop-assisted vapor-liquid-solid growth. Nanodrops with larger diameters are shown to grow longer NWs because growth is governed mainly by direct precursor impingement on the nanodrop surface. The theoretical and experimental results also show that growth phase is dependent on NW diameter. We show that InP NWs with a diameter less than a certain value exhibit coherent growth of a single crystalline wurtzite (WZ) phase, whereas larger diameter InP NWs often contain sequences of WZ and zincblende phases and stacking faults. These findings allow one to achieve coherent NW growth and WZ phases free from twinning if the NW diameter is below certain material-dependent critical diameters.

Molecular beam epitaxy growth of InAs and In[sub 0.8]Ga[sub 0.2]As channel materials on GaAs substrate for metal oxide semiconductor field effect transistor applications

InAs and high indium concentration InGaAs have very high electron mobilities and saturation velocities. Using them as the metal oxide semiconductor field effect transistor (MOSFET) channel materials is a very promising way to keep improving the integrated circuit chip performance beyond Moore’s law. One major obstacle is the growth of these high mobility channel materials on lattice-mismatched substratcs. In this work, we studied the molecular beam epitaxy growth of InAs, In0.8Al0.2As, and In0.8Ga0.2As on lattice-mismatched GaAs substrate using a thin indium-rich InAs wetting layer. Reflection high energy electron diffraction and atomic force microscopy were used to optimize the growth conditions. A surface roughness of ∼0.5nm rms was obtained for InAs layers. A new MOSFET structure with In0.8Ga0.2As channel and In0.8Al0.2As buffer layer was also demonstrated. High mobility depletion mode MOSFET characteristics were demonstrated.

Growth of InSb epitaxial layers on GaAs (0 0 1) substrates by LPE and their characterizations

The growth of epitaxial InSb layers on highly lattice mismatched GaAs substrates has been successfully achieved via the traditional liquid phase epitaxy. Details about nucleation, growth and optimization have been dealt with. High-resolution X-ray diffraction studies on the epilayers reveal all reflections with distinct layer and substrate peaks even up to a highest scattering angle of 153°. However, the layer peaks are considerably broader, indicating extensive dislocations. The average dislocation density was estimated from the Full-width at half-maximum of symmetric reflection. The grown films were n-type and the typical value of the sheet carrier density at 80 K obtained for these samples was 6.12×10 15/cm 2. The Hall mobility at 80 K was 7.058×10 3 cm 2/ Vs . The room-temperature band gap was determined to be 0.198 eV. Raman scattering measurements have also been performed to characterize the grown epilayers.

Fabrication of self-assembled InGaAs, GaAs, and InAs quantum dots by chemical beam epitaxy

We report on the fabrication of self-assembled GaAs, InGaAs and InAs quantum dots (QD) on GaAs(100) via droplet epitaxy and S–K mode growth by chemical beam epitaxy (CBE). Triethylgallium, trimethylindium, monoethylarsine, and arsine were applied as source materials. GaAs and InGaAs quantum dots with diameter 50 nm and density 1×109 cm−2 were grown by Ga droplet formation and the successive supply of source materials without any pre-treatment steps prior to growth. InAs quantum dots were coherently assembled on a lattice-mismatched GaAs substrate without any indication of misfit dislocation in the Stranski–Krastanow (S–K) growth method. The areal density of 40 nm sized InAs islands was obtained up to 1010 cm−2 by changing the deposition thickness. Our results demonstrate that CBE can be a very powerful method for the growth of self-assembled quantum dots.

Growth and characterization of mid-infrared InGaAs/InAlAs strained triple-quantum-well light-emitting diodes grown on lattice-mismatched GaAs substrates

Strained triple-quantum-well In0.9Ga0.1As/In0.8Al0.2As light-emitting diodes were grown on lattice-mismatched GaAs substrates by molecular-beam epitaxy. The diodes exhibit room-temperature external electroluminescent light emission at 2.4 μm with efficiencies up to 6.4×10−5. The maximum output power at room temperature is 1.85 μW under pulsed operation at 150 mA, (1 kHz, 50% duty cycle). Although the diodes have excellent electrical properties, their optical performance is still found to be limited by the nonradiative Shockley–Read–Hall recombination.

Mid-infra-red InGaAs light-emitting diodes for optical gas sensing grown on lattice-mismatched substrates

InGaAs-InAlAs light-emitting diodes were grown on lattice-mismatched GaAs substrates by molecular beam epitaxy. This makes it possible to tune the emission to the desired wavelength by changing the composition of the grown layers. The authors' diodes exhibit efficient room-temperature emission at 1.9 mu m, necessary for optical sensing of water vapour.

A 0.1- mu m gate Al/sub 0.5/In/sub 0.5/As/Ga/sub 0.5/In/sub 0.5/As MODFET fabricated on GaAs substrates

Al/sub 0.5/In/sub 0.5/As/Ga/sub 0.5/In/sub 0.5/As MODFET structures have been successfully grown on lattice-mismatched GaAs substrates with a 3.8% difference of lattice constants. MODFETs fabricated with a 0.12- mu m T-shaped gate demonstrate DC and microwave characteristics comparable to those of Al/sub 0.5/In/sub 0.5/As/Ga/sub 0.5/In/sub 0.5/As MODFETs on lattice-matched InP substrates. A peak extrinsic DC transconductance of 585 mS/mm and a full-channel current of 370 mA/mm are achieved at room temperature. Parasitic substrate conduction, which may be the result of the threading dislocations under the FET bonding pads and the active FET channel, affects the device performance. The MODFET shows a high current-gain cutoff frequency of 117 GHz and a maximum available gain cutoff frequency of 125 GHz. The effects of substrate conduction on microwave performance are also investigated.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>