AlGaSb Layers Research Articles

InAs0.9Sb0.1-based hetero-p-i-n structure grown on GaSb with high mid-infrared photodetection performance at room temperature

We present the design, fabrication, and characterization of middle-wavelength infrared photodetector based on active InAs0.9Sb0.1-based hetero-p-i-n structure grown on GaSb substrate. In this structure, the active absorption layer is sandwiched between thin quaternary p-type and n-type AlInAsSb layers and a heavily doped AlGaSb layer is introduced to reduce dark current. We observed good lattice matching between GaSb substrates and epitaxial layers by high-resolution X-ray diffraction. Photoluminescence (PL) spectrum at 13 K shows a full width at half maximum of ~ 29 meV, demonstrating good quality active absorption layers. The band gap energy of InAs0.9Sb0.1 is derived as ~ 0.322 eV at 0 K by Varshni fitting from PL spectra at different temperatures. A rather flat room-temperature responsivity of ~ 0.8–0.9 AW−1 over a wavelength range of ~ 2.1 µm is demonstrated without antireflection coating. A detectivity of 8.9 × 108 cm Hz1/2 W−1 at 3.5 µm for room-temperature operation is achieved under applied bias of − 0.5 V.

The Effect of Growth Temperature and V/III Flux Ratio of MOCVD Antimony Based Semiconductors on Growth Rate and Surface Morphology

Epitaxial Al x Ga 1-x Sb layers on GaSb and GaAs substrates have been grown by atmospheric pressure metalorganic chemical vapor deposition using TMAl, TMGa and TMSb. Nomarski microscope and a profiler were employed to examine the surface morphology and growth rate of the samples. We report the effect of growth temperature and V/III flux ratio on growth rate and surface morphology. Growth temperatures in the range of 520°C and 680°C and V/III ratios from 1 to 5 have been investigated. A growth rate activation energy of 0.73 eV was found. At low growth temperatures between 520 and 540°C, the surface morphology is poor due to antimonide precipitates associated with incomplete decomposition of the TMSb. For layers grown on GaAs at 580°C and 600°C with a V/III ratio of 3 a high quality surface morphology is typical, with a mirror-like surface and good composition control. It was found that a suitable growth temperature and V/III flux ratio was beneficial for producing good AlGaSb layers. Undoped AlGaSb grown at 580°C with a V/III flux ratio of 3 at the rate of 3.5 μm/hour shows p-type conductivity with smooth surface morphology

Design optimization of vertical nanowire tunneling field-effect transistor based on AlGaSb/InGaAs heterojunction layer

This paper presents the electrical characteristics of vertical nanowire-type tunneling field-effect transistors (VNW TFETs) based on the AlGaSb/InGaAs heterojunction for low-power, high-speed applications. The proposed devices have a very steep junction, based on broken band alignment between the AlGaSb and InGaAs layers. The extremely thin tunneling barrier increases the tunneling probability between the AlGaSb source region and the InGaAs channel region. For this reason, the broken band based on the AlGaSb/InGaAs heterostructure enhances the on-state current (Ion) of the TFETs. To optimize the electrical performance of the proposed device, design optimization using technology computer-aided design (TCAD) simulations is performed. The design variables are gate length, doping concentrations, and the nanowire radius. The optimized device has a gate length of 30 nm, channel and drain doping concentrations of 1018 cm−3, and a radius of 10 nm. Results confirm that the optimized TFET has a subthreshold swing (S) of 27.8 mV/dec and an Ion value of 2.57 mA/μm.

Method of determination of AlGaAsSb layer composition in molecular beam epitaxy processes with regard to unintentional As incorporation

The accurate determination of the chemical composition of multicomponent antimonide layers still remains difficult. The problem becomes even more complicated when group III antimonides are grown in a MBE chamber that is also used for the growth of group III arsenides. In this paper, the composition of MBE grown AlGaAsSb layers is investigated in the context of unintentional arsenic incorporation. Control of the As concentration and a determination of the AlGaSb composition are crucial for an accurate calculation of the AlGaAsSb stoichiometry. It has been found that when using diffraction measurements with an As detection limit of 0.087%, the Al content in Al0.5Ga0.5Sb is determined with an accuracy of ±1%. Taking into account the GaSb reference from secondary ion mass spectrometry, the accuracy can be increased to ±0.52% of Al. The Al/Ga ratio determined for AlGaSb layers is further used for the calculation of the As content in AlGaAsSb alloys grown under the same technological conditions as the ternary layer. As a result, the procedure for the accurate determination of stoichiometry coefficients in this material is recommended.

Growth of low defect AlGaSb films on Si (1 0 0) using AlSb and InSb quantum dots intermediate layers

We have investigated the structural properties of AlGaSb films grown on Si (100) substrates with multi-buffer layers (GaSb/AlSb/GaSb) inserting a thin AlSb and InSb quantum dots (QDs) inter-buffer layer. Atomic force microscopy measurements of the buffer layers with the QDs inter-buffer layer showed the mirror-like surface with a low defect density. Also, the surface roughness of a resulting AlGaSb film on the buffer layers with the QDs inter-buffer layer is decreased by a factor of about 10 compared with the roughness of the film without the QDs interlayer. In addition, X-ray diffraction rocking curve result showed that the structural properties of AlGaSb layer with the QDs interlayer were improved significantly. We suggest that the significant reduction of the dislocation density in the AlGaSb film was due to the dislocations being prevented from propagating into the AlGaSb overlayer by the thin AlSb and InSb QDs interlayer.

Growth of AlGaSb Compound Semiconductors on GaAs Substrate by Metalorganic Chemical Vapour Deposition

EpitaxialAlxGa1-xSb layers on GaAs substrate have been grown by atmospheric pressure metalorganic chemical vapour deposition using TMAl, TMGa, and TMSb. We report the effect of V/III flux ratio and growth temperature on growth rate, surface morphology, electrical properties, and composition analysis. A growth rate activation energy of 0.73 eV was found. For layers grown on GaAs at 580∘C and 600∘C with a V/III ratio of 3 a high quality surface morphology is typical, with a mirror-like surface and good composition control. It was found that a suitable growth temperature and V/III flux ratio was beneficial for producing good AlGaSb layers. Undoped AlGaSb grown at 580∘C with a V/III flux ratio of 3 at the rate of 3.5 μm/hour shows p-type conductivity with smooth surface morphology and its hole mobility and carrier concentration are equal to 237 cm2/V.s and 4.6 × 1017 cm-3, respectively, at 77 K. The net hole concentration of unintentionally doped AlGaSb was found to be significantly decreased with the increased of aluminium concentration. All samples investigated show oxide layers (Al2O3,Sb2O3, andGa2O5) on their surfaces. In particular the percentage of aluminium-oxide was very high compared with a small percentage of AlSb. Carbon content on the surface was also very high.

Growth of InAs Quantum Dots on a Low Lattice-Mismatched AlGaSb Layer Prepared on GaAs (001) Substrates

Optical communication wavelength emissions from the quantum dots (QDs) structures prepared on (001)-oriented GaAs substrates are discussed. A new growth technique of low-stressed InAs QDs on the AlGaSb layer in a low lattice-mismatched (1.3%) InAs/AlGaSb system is presented. The average height and diameter of the 4-ML InAs QDs on AlGaSb are evaluated to 5.8 nm and 45.2 nm respectively with an average density of 2.18 x 1010 /cm2 using atomic force microscope (AFM) measurements. There is structural selectivity between the QDs layer and the flat hetero-interface under changing growth conditions in the InAs/AlGaSb system. Long-wavelength PL emissions around 1.3 µm and 1.55 µm can be achieved by embedding InAs QDs in AlGaSb layers. Therefore it is expected that low-stressed InAs QDs grown on a AlGaSb layer prepared on a GaAs substrate will be useful in the fabrication of novel QDs devices for optical-communication networks.

Characterization of GaSb-based heterostructures by scanning electron microscopecathodoluminescence and scanning tunnelling microscope

The luminescence of GaSb and AlGaSb layers grown on GaAs substrates by metal organicvapour phase epitaxy has been studied by means of cathodoluminescence (CL) using ascanning electron microscope. CL plane-view analysis reveals a distribution of defects, asmisfit dislocations, in some of the structures. The luminescence bands observed in theGaSb layers are related to near band edge recombination and to an excess of Ga. In thecase of AlGaSb/GaSb heterostructure emission bands related to the ternary compound andto donor–acceptor recombination are detected. In addition, with the aid of a scanningtunnelling microscope (STM), local electronic properties, such as conductance and surfaceenergy gap, were studied in sample cross-sections. The results obtained from imagingand spectroscopy modes of STM enabled us to image the single AlGaSb layer.

Transport properties in asymmetric InAs/AlSb/GaSb electron-hole hybridized systems

Transport properties in asymmetric InAs/GaSb and InAs/AlSb/GaSb heterostructures sandwiched by AlGaSb layers were studied. For the InAs/GaSb structures, partially compensated quantum Hall effects arising from the electron-hole hybridization were observed. By changing the thickness of each layer, the energy positions of the conduction band and the valence band can be controlled independently. In InAs/AlSb/GaSb structures, we tried to control the hybridization strength by varying the AlSb barrier thickness. Magnetoresistance measurements, in which the magnetic field was applied perpendicular and parallel to the surface, and cyclotron resonance (CR) measurements show that there is a clear transition from the electron-hole-hybridized system to the electron-hole-independent system. The transition point appeared at around the 2-nm-barrier thickness in all experiments, suggesting a dominant role of the overlap of electron and hole wave functions. According to the absorption peak shapes in the CR measurements, the hybridized system can be further classified as strongly hybridized or weakly hybridized. Only in the weakly hybridized system was the Shubnikov--de Haas--like oscillation due to the short-range scattering by the hole potential observed in the electron CR absorption peak.

Study of optical and electrical properties of AlxGa1−xSb grown by metalorganic chemical vapor deposition

AlxGa1−xSb films in the regime 0×0.25 have been grown by metalorganic chemical vapor deposition on GaAs and GaSb substrates using TMAl, TMGa, and TMSb precursors. We report growth conditions and film properties, including the effect of V/III ratio and growth temperature on electrical and optical properties. Growth temperatures in the range of 520°C and 680°C and V/III ratios from 1 to 5 have been investigated. All epilayers grown exhibit p-type behavior. The mobility decreases and the carrier concentration increases sharply when a small amount of Al is incorporated into GaSb. The sharp cutoff and Fabry-Perot oscillations of the transmission spectra of the AlGaSb layers confirm the high quality of the films. The principle photoluminescence features observed are attributed to bound exciton and donor-acceptor transitions with FWHM comparable to the best values reported elsewhere.

Study of persistent photoconductivity in semimetallic Al0.2Ga0.8Sb/InAs quantum wells

The “positive” persistent photoconductivity (PPC) and “negative” persistent photoconductivity (NPPC) have been observed in Al0.2Ga0.8Sb/InAs quantum wells. The decay kinetics of the PPC and NPPC effects can be well described by stretched-exponential functions and the activation energy of the thermally activated relaxation was obtained. Through the studies of the NPPC and PPC effects under various conditions, such as different temperature and different photon energy of excitation, we suggest that the NPPC and PPC effects are caused by two competing processes. At T≤40K, the electrons in the InAs wells are excited into the valence band of the AlGaSb layer, the recovery to the original state is prohibited by the barrier due to interface band bending and hence NPPC effects occur. At T≥140K, the photoexcited holes are trapped by the deep defects in the InAs well and the remaining electrons contribute to the observed PPC. For 40K<T<140K, these two mechanisms compete with each other. The previously proposed model that describes the NPPC resulting from the capture of the photoexcited electrons by the DX-like deep donors in AlGaSb fails to explain our observation here.

AFM fabrication and characterization of InAs/AlGaSb nanostructures

We describe two distinct fabrication processes based on atomic force microscope (AFM) oxidation for nanoscale device fabrication which are particularly useful for GaSb/AlGaSb/InAs heterostructures. One utilizes water immersion which selectively removes the oxidized GaSb region. The other makes use of the enhanced etching rate for oxidized GaSb and AlGaSb layers for a developer solution resulting in the formation of deep grooves down to the InAs channel layer. The latter is used together with a selective InAs etching for the formation of a narrow constricted structure. A 0.3- μm-period corrugation on the GaSb surface is fabricated by the former process in order to make a two-dimensional electron gas (2DEG) with its electron concentration laterally modified. The magnetotransport measurements of the structure show Weiss oscillations corresponding to the corrugation period verifying the successful formation of the laterally modified 2DEG. A single electronic device structure fabricated by the latter shows non-linear I– V characteristic behavior indicating the capability of these AFM oxidation processes for the fabrication of various types of nanostructure devices.

High quality AlGaSb, AlGaAsSb and InGaAsSb epitaxial layers grown by liquid-phase epitaxy from Sb-rich melts

The paper is concerned with the study of the growth of AlGaSb, AlGaAsSb and InGaAsSb epilayers, which are lattice-matched to GaSb, by means of liquid-phase epitaxy (LPE) from Sb-rich melts. The obtained composition ranges were 0.02 ≤ x ≤ 0.20 for AlxGa1–xSb, AlxGa1–xAsySb1–y epilayers and 0.04 ≤ x ≤ 0.24 for InxGa1–xAsySb1–y layers. In the PL spectra measured on AlGaSb and GaInAsSb direct-gap solid solutions, only peaks with a maximum corresponding to the bandgap were observed. No long-wavelength peaks, which correspond to defects such as VGa+GaSb and are typical of GaSb and related solid solutions grown from In- or Ga-rich melts, were found in PL spectra of the epilayers obtained.

The n-type and p-type doping of GaSb and AlGaSb grown by metalorganic molecular beam epitaxy

The n-type and p-type doping characteristics are studied in the MOMBE (metalorganic molecular beam epitaxy) growth of GaSb and AlGaSb. Unintentionally doped GaSb and AlGaSb show p-type conduction. Higher hole concentration GaSb layers are obtained for lower growth temperatures and higher Sb flux. Highly p-doped (⪢ 10 18 cm −3) AlGaSb layers are obtained, especially for high Al mole fraction (⪢ 25%), due to the uptake of carbon generated by the decomposition of the metalorganic sources (triethylgallium). n-Type GaSb and AlGaSb layers are grown using GaTe as a dopant source. High electron concentrations above 2 × 10 18 cm −3 are obtained. SIMS (secondary ion mass spectrometry) measurements show that the activation energy for the incorporation of Te into GaSb is 1.83 eV. This value is different from that in elemental source MBE with the same GaTe as a Te source. This difference is discussed in relation to the growth mechanism.

Electrical and photoluminescent properties of high-quality GaSb and AlGaSb layers grown from Sb-rich solutions by liquid-phase epitaxy

The growth-temperature dependence of electrical and photoluminescent (PL) properties of GaSb and Al0.065Ga0.935Sb layers grown from Sb-rich solutions by liquid-phase epitaxy has been studied. The GaSb and AlGaSb epitaxial layers grown at 606 °C exhibit a low hole concentration of 4×1015 and 2×1016 cm−3, respectively. The low-temperature PL spectra of GaSb and AlGaSb is dominated by free-exciton transition and excitons bound to neutral acceptors. As the growth temperature is increased, both the residual hole concentration and the intensity of band A related to native lattice defects in GaSb and AlGaSb increase. The high-quality GaSb and AlGaSb epitaxial layers can be grown at low temperatures from Sb-rich solutions.

Morphological Evolution and Properties of LPE Grown GaSb, AlGaSb and AlGaAsSb

ABSTRACTThe nucleation morphologies of LPE grown GaSb, AlGaSb and AlGaAsSb layers on GaSb substrates are presented. The morphology of the GaSb layers grown from Sb-rich melts showed facets on highly terraced surface, whereas those grown from Ga-rich melts exhibited fine terraces without facets. An optimum temperature in the range of 500 – 550°C was found to be suitable for the growth of mirror smooth layers from Ga-melts. The surface morphology of the AlxGa1-xSb layers degrades drastically with increase in Al content beyond x = 0.5. The surface morphology of AlGaAsSb epilayers has been found to depend strongly on the pre-growth melt dissolution sequence.

MOMBE growth of AlSb and AlGaSb using trimethylamine alane

MOMBE (metalorganic molecular beam epitaxy) growth of AlSb and AlGaSb using trimethylamine alane (TMAAl), triethylgallium (TEGa) and solid antimony (Sb 4) is reported for the first time. The growth rate of AlSb shows a monotonic increase with substrate temperature ( T sub) and a decrease with increasing Sb flux. The activation energy for the AlSb growth is 14 kcal/mol at T sub > 460°C and 30 kcal/mol at T sub<460°C. In the AlGaSb growth, the enhancement of the partial growth rate of GaSb is observed and is caused by the TEGa decomposition enhancement effect of the hydrogen atoms from AlH 3. 4.2 K photoluminescence (PL) spectra for the undoped AlGaSb layers exhibit a sharp band-to-band transition with an intensity comparable to that for the GaSb bulk crystal.