The effect of trimethylaluminum concentration on the incorporation of P In AlxGa1−xPyAs1−y grown by organometallic vapor phase epitaxy

The organometallic vapor phase epitaxial (OM-VPE) growth of Al_xGa_1-xP_yAs_1-y on graded GaP_yAs_1-yGaAs in the compositional range 0 < x < 0.9 and 0 < y < 0.6 is reported. It is found that composition control can be easily achieved, and that the vapor phase ratio of trimethylaluminum to trimethylgallium strongly influences the incorporation of P in the solid. A model is developed which explains this in terms of competing reaction rates. The model gives a good fit to the experimental data.     

Impurity-induced disordering of AlxGa1−xAs-GaAs quantum well heterostructures with (Si2)x(GaAs)1−x barriers

Recent work indicates that the alloy (Si₂)_x(GaAs)_1−x can be formed within the GaAs quantum well of an Al_xGa_1−xAs-GaAs quantum well heterostructure (QWH) and results in a shift of laser operation to higher energy. In this paper we show, by SIMS and EDS measurements, that the Si concentration in the (Si₂)_x(GaAs)_1−x layer far exceeds typical “doping” levels. The stability of these QWHs has been investigated with respect to thermal annealing and Zn impurity-induced layer disordering (Zn-IILD). Data are presented showing that the (Si₂)_x(GaAs)_1−x alloy is stable against thermal annealing unless a rich source of Ga vacancies is provided, and that relatively low temperature Zn diffusion greatly enhances the disordering process of the alloy layer.     

High performance AlyGa1−yAs-GaAs-lrxGa1−xAs quantum well lasers defined by silicon-oxygen impurity-induced layer disordering

In these experiments impurity-induced layer disordering (IILD) utilizing chemical reduction of SiO₂ by Al (from Al_0.8Ga_0.2As) is employed to generate Si and O to effect layer disordering. The SiO₂-Al_0.8Ga_0.2As reaction is studied with respect to annealing ambient. By controlling the extent of disordering via As₄ overpressure, closely spaced (∼1μm) Si-O IILD buried heterostructure lasers can be optically coupled or uncoupled. Direct observation of O incorporation into the buried layers is shown using secondary ion mass spectroscopy (SIMS). The thermal stability of separate-confinement Al_yGa_1−yAs-GaAs-In_xGa_1−xAs quantum well heterostructure (QWH) laser crystals is investigated using SIMS, transmission electron microscopy (TEM), and photoluminescence (PL) measurements. The data show that the thermal stability of a strained-layer In_0.1Ga_0.9As quantum well (QW) is strongly dependent upon: (1) the layer thickness and heterointerfaces of the Al_yGa_1−yAs-GaAs waveguide layers located directly above and below the QW, (2) the type of surface encapsulant employed, and (3) the annealing ambient. Narrow single-stripe (<2μm) lasers fabricated via Si-O diffusion and layer disordering exhibit low threshold currents (I_th ∼ 4 mA) and differential quantum efficiencies,η, of 22% per facet under continuous (cw) room-temperature operation.     

Investigation on resonant tunneling in GaAs/AlxGa1-xAs DBD using tunneling spectroscopy

 Experimental investigation on resonant tunneling in various GaAs/Al_xGa_(1-x)As double barrier single well structures has been performed by using tunneling spectroscopy at different temperatures.The results show that in addition to resonant tunneling via GaAs well state confined by Al_xGa_(1-x)As Γ-point barrier there exists resonant tunneling via GaAs well state confined by Al_xGa_(1-x)As X-point barrier for both indirect(x>0.4)and direct(x<0.4)cases.     

A novel pseudomorphic (GaAs1−xSbx-InyGa1−yAs)/GaAs bilayer-quantum-well structure lattice-matched to GaAs for long-wavelength optoelectronics

Two types of quantum well (QW) structures grown lattice matched on (100) GaAs have been studied. The first type of structure consists of pseudomorphic GaAs_xSb_1-x/GaAs (x≤0.3) SQWs which show emission wavelengths longer than those reported for pseudomorphic In_yGa_1−yAs/GaAs QWs. However, the attractive emission wavelength of 1.3 μm has not been achieved. To reach this goal, a novel type of bilayer QW (BQW) has been grown consisting of a stack of two adjacent pseudomorphic layers of GaAs_xSb_1−x and In Ga_1-y As embedded between GaAs confinement layers. In this BQW, a type-II heterojunction is formed between GaAs_xSb_1−x and In_yGa_1−yAs, resulting in a spatially indirect radiative recombination of electrons and holes at emission wavelengths longer than those achieved in the GaAs_xSb_1−x/GaAs and Ii_yGa_1−yAs/GaAs SQWs. The longest 300K emission wavelength observed so far was 1.332 μm.     

Properties of Ge-doped GaAs and Alx Ga1−xAs,Sn-doped Alx Ga1−xAs and Si-Te-doped GaAs

In order to better understand the electrical and optical properties of GaAs and Al_xGa_1-x As used in making double heterojunction lasers, we have studied the Hall coefficient, resistivity and photoluminescence behavior of doped epitaxial samples of these materials. In particular, we report results on Ge-doped GaAs and Al_x Ga_1-x As, Sn-doped Al_xGa_1-x As and Si-Te-doped GaAs single crystal layers which were grown on GaAs substrates by the liquid phase epitaxial method. The effects of impurities in the solution on the carrier concentration, mobility, photoluminescence spectra and possible recombination processes in these layers are discussed.     

Properties and use of ln0.5(AlxGa1-x)0.5P and AlxGa1-x as native oxides in heterostructure lasers

Data are presented demonstrating the formation of native oxides from high Al composition In_0.5(Al_xGa_1-x)_0.5P (x≳ 0.9) by simple annealing in a “wet” ambient. The oxidation occurs by reaction of the high Al composition crystal with H₂O vapor (in a N₂ carrier gas) at elevated temperatures (≥500° C) and results in stable transparent oxides. Secondary ion mass spectrometry (SIMS) as well as scanning and transmission electron microscopy (SEM and TEM) are employed to evaluate the oxide properties, composition, and oxide-semiconductor interface. The properties of native oxides of the In_0.5(Al_xGa_1-x)_0.5P system are compared to those of the Al_xGa_1-xAs system. Possible reaction mechanisms and oxidation kinetics are considered. The In_0.5(Al_xGa_1-x)_0.5P native oxide is shown to be of sufficient quality to be employed in the fabrication of stripe-geometry In_0.5(Al_xGa_1-x)_0.5P visible-spectrum laser diodes.     

Wavelength tuning in strained layer InGaAs-GaAs-AlGaAs quantum well lasers by selective-area MOCVD

Selective-area growth and regrowth using conventional atmospheric pressure metalorganic chemical vapor deposition is investigated for wavelength tuning in strained layer In_xGa_1-xAsGaAs-Al_y Ga_1-yAs quantum well lasers. Growth inhibition from a silicon dioxide mask is the mechanism used for the selective-area growth rate enhancement. By varying the width of the oxide stripe opening, differences in the growth rate yield different quantum well thicknesses, and hence different lasing wavelengths for devices on the same wafer. Both two-and three-step growth processes are utilized for selective-area epitaxy of strained layer In_xGa_1-xAs-GaAs quantum well active regions, with lasers successfully fabricated from the three-step growth. Scanning electron microscopy and transmission electron microscopy indicate that the absence of an oxide mask during Al_yGa_1-yAs growth is essential for successful device operation. A wide wavelength tuning range of over 630Å is achieved for lasers grown on the same substrate.     

Nickel silicidation techniques for strained Si1?xGex, Si1?x?yGexCy, and Si1?yCy alloys material-device applications

A nickel silicide process for Si_1-xGe_x, Si_1-x-yGe_xC_y, and Si_1-yC_y alloy materials compatible with Si technology has been developed. Low-resistivity-phase (12–20 μΘ cm) nickel silicides have been obtained for these alloys with different low sheet-resistance temperature windows. The study shows that thin (15–18 nm) silicide layers with high crystalline quality, smooth silicide surface, and smooth interface between silicide and the underlying material are achievable. The technique could be used to combine the benefits of Ni silicide and Si_1-xGe_x, Si_1-x-yGe_xC_y, and Si_1-yC_y alloys. The technique is promising for Si or Si_1-xGe_x, Si_1-x-yGe_xC_y, and Si_1-yC_y alloy-based metal-oxide semiconductor, field-effect transistors (MOSFETs) or other device applications.     

Calculation of energy band gaps in quaternary iii/v alloys

The dielectric theory of electronegativity is applied to the calculation of the compositional dependence of the energy band gap for quaternary III/V alloys of type A_l-xB_xC_1-yD_y and A_1-x-yB_xC_yD. The departure from linearity of E_G versus x and y is taken to be the sum of two terms, the intrinsic or virtual crystal term and the extrinsic term due to effects of aperiodicity which for one type of alloy may occur on both sublattices. Rather than simply treating the quaternary as an average of the bounding ternary systems, as has been common in the past, the intrinsic departure from linearity is calculated by assuming E_h,i,C, and D_av to vary linearly with x and y. The result is a smaller intrinsic deviation from linearity and a much better fit to existing data in the system Ga_1-xIn_xAs_1-y P_y. The calculation is also applied to three systems where no data exist but which are of great interest because of their potential application for the fabrication of lattice matched tandem solar cells: Ga_l-xA1_xAs_l-ySb_y. Ga_1-x-yA1_xIn_yAs, and GaAs_1-x-yP_xSb_y.     

Improved quality of AlxGa1−x as grown on se-Doped AlxGa1−x as substrate-Layers by metalorganic chemical vapor deposition

Al_xGa_1−xAs epilayers were grown directly on different Al_xGa_1−xAs substrate-layers by metalorganic chemical vapor deposition (MOCVD). The quality of Al_xGa_1−-xAs layers was significantly improved when Se-doped Al_xGa_1−xAs substrate-layers were used. Al_0.13Ga_0.87As epilayers with excellent morphology, optical, and crystal quality were grown on Se-doped Al_0.26Ga_0.74As. The full width at half maximum of the bound exciton peak as low as 4.51 meV was measured by low-temperature (14.9K) photoluminescence. The improvement is attributed to a Se passivation effect at the surface of Se-doped Al_xGa_1−xAs substrate-layers. Results suggest that Se will reduce and delay the formation of native oxides.     

Controlled oxygen incorporation in indium gallium arsenide and indium phosphide grown by metalorganic vapor phase epitaxy

The defect engineering in metalorganic vapor phase epitaxy In_xGa_1-xAs and InP by controlled oxygen doping using diethyl aluminum ethoxide (DEALO) was developed in this study. DEALO doping has led to the incorporation of Al and O, and the compensation of shallow Si donors in In_xGa_1−xAs: Si with 0 ≤ x ≤ 0.25. With the same DEALO mole fraction during growth, the incorporation of Al and O was found to be independent of x, but the compensation of Si donors decreases with increasing In content. Deep level transient spectroscopy analysis on a series of In_xGa_1-xAs: Si. samples with 0 ≤ x ≤ 0.18 revealed that oxygen incorporation led to a set of deep levels, similar to those found in DEALO doped GaAs. As the In composition was increased, one or more of these deep levels became resonant with the conduction band and led to a high electron concentration in oxygen doped In_0.53Ga_0.47As. Low temperature photoluminescence emission measurements at 12K on the same set of samples revealed the quenching of the near-band edge peak, and the appearance of new oxygen-induced emission features. DEALO doping in InP has also led to the incorporation of Al and O, and the compensation of Si donors due to oxygen-induced multiple deep levels.     

Reduction of deep levels in MOCVD-regrown AlxGa1−x as interfaces by (NH4)2S passivation and in-situ HCl etching

The effects of surface preparation usinginsitu HCl etching and (NH₄)₂S passivation of Al_xGa_1-xAs episurfaces prior to regrowth by MOCVD are analyzed by deep level transient spectroscopy (DLTS), electrochemical profiling (C-V) and room-temperature photoluminescence (PL). Four electron traps were found from the DLTS measurements; a DX-center and three traps previously reported for oxygen-contaminated MOCVD systems. Electrical and optical measurements on quantum well lasers containing a regrown interface in the optical confinement region are also presented. It is demonstrated that both (NH₄)₂S passivation and HClin-situ etching improve the electrical and optical quality of the regrown Al_xGa_1-xAs interfaces, with the best results being obtained when the two methods are used in tandem.     

Diffusion of zinc into gaas through Al0.3Ga00.7As

The diffusion of zinc into GaAs, Al_0.3Ga_0.7As and Al_0.3Ga_0.7As/GaAs single heterostructures have been studied. The depth of the diffusion front is found to be proportional to the square root of the diffusion time, [t]^1/2, and for single heterostructures the Al_0.3Ga_0.7As layer thickness,d ₁ modifies this relationship through decreasing the junction depth byd ₁ multiplied by a constant. It is shown that this relationship can be used for predicting diffusion fronts in double heterostructures.     

A composition-dependent model for the complex dielectric function of In1 xGaxAsyP1− y lattice-matched to InP

Accurate and numerically efficient models for the complex dielectric function vs wavelength and material characteristics are essential for the use of nondestructive optical techniques such as spectroscopic ellipsometry or reflectometry. These optical techniques are commonly used for real-time and run-to-run monitoring and control of growth and etch processes to determine a material's composition and thickness. In this work, we discuss an improved composition-dependent model for the complex dielectric function for lattice-matched In_1-xGa_xAs_yP_1-y/InP systems valid over the entire composition range 0 ≤ y ≤ 1. We describe our model, which is an extension of the critical point parabolic band method and is based on the model proposed by Charles Kim et al. for the A_xGa_1-x/GaAs system. We demonstrate the quality of the model in fitting optical data for individual compositions and compare our results to other established models including the harmonic oscillator approximation and the model of Adachi. Using results obtained from the individual fits, we generate a composition-dependent model that is valid for the entire range of lattice-matched compositions. Also, we show how this model can be used to accurately determine the composition (±0.01) of an unknown material whose dielectric response has been obtained using spectroscopic ellipsometry or a similar technique.     

Group-V composition control for InGaAsP grown by gas source molecular beam epitaxy

Based on our kinetics models for gas source molecular beam epitaxy of mixed group-V ternary materials, the group-V composition control in In_yGa_1−yAs_1−xP_x epilayers has been studied. The P or As composition in In_yGa_1−yAs_1−xP_x (lattice matched to InP or GaAs) can be obtained from a simple equation for substrate temperatures below 500°C. This has been verified by a series of experimental results.     

Alkoxide precursors for controlled oxygen incorporation during metalorganic vapor phase epitaxy GaAs and AlxGa1−xAs growth

Controlled oxygen incorporation in GaAs using Al-0 bonding based precursors, dimethyl aluminum methoxide (DMALO) and diethyl aluminum ethoxide (DEALO), is presented in this investigation. A comparison study of oxygen incorporation kinetics between nominally undoped Al_xGa_1−xAs using trimethyl aluminum and DMALO-doped GaAs suggests that DMALO is one of the most important oxygen-bearing agents responsible for unintentional oxygen incorporation in Al_xGa_1−xAs. Controlled oxygen doping using DEALO is reported for the first time. Oxygen incorporation behavior, especially on the effect of the V/III ratio, was found to be quite different from the case of DMALO, mainly due to the differences between methyl- and ethyl-based growth chemistries. Physical, electrical, and optical properties of these oxygen-doped GaAs are also reported.     

Enhanced/suppressed interdiffusion of InGaAs-GaAs-AlGaAs strained layers by controlling impurities and gallium vacancies

The interdiffusion of In and Ga at an InGaAs-GaAs interface subjected to different annealing temperatures, times, and environments is demonstrated. The interdiffusion coefficients and activation energies are determined by correlating the shift in the photoluminescence peaks with the calculated quantum well transition energies based on an error function composition profile. The results indicate that a higher In composition In_xGa_1-xGaAs single quantum well (SQW) leads to a higher interdiffusion coefficient of In and Ga in an As overpressure annealing condition. Also, As overpressure increases the interdiffusion, whereas Ga overpressure reduces the interdiffusion. The thermal activation energies for different In composition InGaAs-GaAs SQW’s (x = 0.057, 0.10, 0.15) range from 3.3 to 2.6 eV for an As overpressure environment and from 3 to 2.23 eV for the Ga overpressure situation. With respect to impurity induced disordering by Zn using a Ga or As overpressure significantly effects the depth of the Zn diffusion front but significant mixing does occur in either case when the impurity front reaches the quantum well.     

Electrical and optical properties of N-type Alx Ga1-x as grown by MO-VPE

Growth conditions and properties of Al_xGa_1-xAs (0.1 ≤ × ≤O.3) using metalorganic vapour phase epitaxy (MO-VPE) are investigated. N-type is achieved either by silicon or by selenium doping. Properties of the layers are evaluated by Hall effect, cathodoluminescence and photoluminescence. It is shown that selenium doping leads to luminescent material : when x = O.1, the efficiency is only a factor of 2 smaller than for GaAs. Deposition temperature is a critical parameter : increasing the growth temperature yields more luminescent Al_x Ga_1-x As. This work has been partly supported by the Délégation à la Recherche Scientifique et Technique (D.G.R.S.T.)     

Effect of Se-doping on deep impurities in AlxGa1−xAs grown by metalorganic chemical vapor deposition

We have studied the effect of Se-doping on deep impurities in Al_xGa_1−xAs (x = 0.2∼0.3) grown by metalorganic chemical vapor deposition (MOCVD). Deep impurities in various Se-doped Al_xGa_1−xAs layers grown on GaAs substrates were measured by deep level transient spectroscopy and secondary ion mass spectroscopy. We have found that the commonly observed oxygen contamination-related deep levels at E_c-0.53 and 0.70 eV and germanium-related level at E_c-0.30 eV in MOCVD grown Al_xGa_1−xAs can be effectively eliminated by Se-doping. In addition, a deep hole level located at E_y + 0.65 eV was found for the first time in Se-doped Al_xGa_1-xAs when Se ≥2 × 10¹⁷ cm⁻³ or x ≥ 0.25. The concentration of this hole trap increases with increasing Se doping level and Al composition. Under optimized Se-doping conditions, an extremely low deep level density (N_t less than 5 × 10¹² cm⁻³, detection limit) Al_0.22Ga_0.78As layer was achieved. A p-type Al_0.2Ga_0.8As layer with a low deep level density was also obtained by a (Zn, Se) codoping technique.