Intentional ρ-type doping by carbon in metalorganic MBE of GaAs

We report on the intentional ρ-type doping of GaAs layers grown in an UHV system from molecular beams of arsine (AsH₃) and mixtures of frimethyl gallium (TMG) and friethyl gallium (TEG). The entire doping range between 10¹⁴ cm^-3 (growth from pure TEG) and 10²⁰ cm^-3 (growth from pure TMG) can be covered by using mixtures of TMG and TEG. As revealed by SIMS and photoluminescence (PL) carbon is the dominant acceptor in the layers. Comparison of the Hall mobility and of the PL spectra shows that the quality of our films equals that of the best LPE and MBE grown ρ-type GaAs layers.     

High electron mobility in (InAs)n(GaAs)n short period superlattices grown by MOVPE for high-electron mobility transistor structure

(InAs)_n(GaAs)_n short period superlattices (SPSs) have been successfully grown by a continuous MOVPE process on InP substrates. Their structural, optical, and electrical properties have been studied. The periodic structures have been confirmed by x-ray measurements and (InAs)₁(GaAs)₁ SPSs have been clearly observed by transmission electron microscopic characterization. The optical quality of the material has been tested by 2K photoluminescence and excitonic recombinations have been observed. Mobilities as high as 10700 cm².V⁻¹.s⁻¹ and 64000 cm². V⁻¹.s⁻¹ for a sheet concentration of 3 × 10¹² cm⁻² have been obtained at 300K and 77K, respectively.     

Arsenic cluster superlattice in gallium arsenide grown by low-temperature molecular-beam epitaxy

Molecular-beam epitaxy at 200 °C is used to grow an InAs/GaAs superlattice containing 30 InAs delta-layers with a nominal thickness of 1 monolayer, separated by GaAs layers of thickness 30 nm. It is found that the excess arsenic concentration in such a superlattice is 0.9×10²⁰ cm⁻³. Annealing the samples at 500 and 600 °C for 15 min leads to precipitation of the excess arsenic mainly into the InAs delta-layers. As a result, a superlattice of two-dimensional sheets of nanoscale arsenic clusters, which coincides with the superlattice of the InAs delta-layers in the GaAs matrix, is obtained. Fiz. Tekh. Poluprovodn. 32, 1161–1164 (October 1998)     

ZnSe heteroepitaxy on GaAs (110) substrate

ZnSe heteroepitaxial layers have been grown on GaAs (100), (110) on axis, and (110) 6° miscut substrates by molecular beam epitaxy. ZnSe on GaAs (110) shows smooth and featureless spectra from Rutherford backscattering channeling measurements taken along major crystalline directions, whereas ZnSe on GaAs (100) without pre-growth treatments exhibit large interface disorder in channeling spectra. ZnSe films grown on GaAs (110) on axis show facet formation over a wide range of growth conditions. The use of (110) 6° miscut substrates is shown to suppress facet formation; and under the correct growth conditions, facet-free surfaces are achieved. Etch pit density measurements give dislocation densities for ZnSe epitaxial layers grown on GaAs (100), (110) on axis, and (110) 6° miscut substrates of 10⁷/cm², 3 × 10⁵/cm² and 5 × 10⁴/cm², respectively. These results suggest that with further improvements to ZnSe growth on GaAs (110)-off substrates it may be possible to fabricate defect free ZnSe based laser devices.     

Preparation and properties of Mn-doped epitaxial gallium arsenide

The preparation of manganese-doped GaAs epitaxial layers growth from the liquid-phase, and Hall effect and resistivity measurements in the temperature range from 60 to 300°K, are described. An anomalous solubility of GaAs in the Ga + GaAs + Mn solution was observed and occurrence of a Mn₂As-phase in solution was identified. From the analysis of the Hall effect measurements the thermal activation energy of the manganese acceptor was determined. The energy decreases from 0·092 to 0·084 eV with the Mn-concentration in the epitaxial layers increasing from 6 × 10¹⁷ cm^?3 to 3 × 10¹⁹ cm^?3. The solubility of Mn in GaAs at the temperature of the preparation (850°C) was found to be about 4 × 10¹⁹ cm^?3.     

Metalorganic chemical vapor deposition growth of GaAs:Er using Er(C4H9C5H4)3

Erbium doped GaAs has been grown by metalorganic chemical vapor deposition using a novel liquid precursor: Tris (n-butylcyclopentadienyl) erbium, Er(C₄H₉C₅H₄)₃. Erbium doping as high as 1.2 × 10¹⁹cm⁻³ has been realized. The morphology was excellent at growth temperatures near 620°C. The erbium concentration was found to depend on growth temperatures due to incomplete pyrolysis of the erbium metalorganic compound. The erbium-related PL intensity was decreased when the erbium concentration exceeded ∼1.2 × 10¹⁹cm⁻³.     

Si-implantation into GaAs grown on Si

200 keV Si implantations were performed in the dose range of 5 × 10¹² − 1 × 10¹⁴ cm⁻² in GaAs grown on Si. For comparison implants were also performed in GaAs layers grown on GaAs substrates. Implanted layers were annealed by both furnace and halogen lamp rapid thermal anneals. Significantly lower donor activations were observed in GaAs layers grown on Si substrates than in the layers grown on GaAs substrates. Extremely low dopant activations were obtained for Be implants in GaAs grown on Si. Photoluminescence and photoreflectance measurements were also performed on the implanted material.     

Study of the Structural and Luminescence Properties of InAs/GaAs Heterostructures with Bi-Doped Potential Barriers

The influence of Bi in GaAs barrier layers on the structural and optical properties of InAs/GaAs quantum-dot heterostructures is studied. By atomic-force microscopy and Raman spectroscopy, it is established that the introduction of Bi into GaAs to a content of up to 5 at % results in a decrease in the density of InAs quantum dots from 1.58 × 10¹⁰ to 0.93 × 10¹⁰ cm^–2. The effect is defined by a decrease in the mismatch between the crystal-lattice parameters at the InAs/GaAsBi heterointerface. In this case, an increase in the height of InAs quantum dots is detected. This increase is apparently due to intensification of the surface diffusion of In during growth at the GaAsBi surface. Analysis of the luminescence properties shows that the doping of GaAs potential barriers with Bi is accompanied by a red shift of the emission peak related to InAs quantum dots and by a decrease in the width of this peak.     

Growth and characterization of large diameter undoped semi-insulating GaAs for direct ion implanted FET technology

The growth of large diameter, semi-insulating GaAs crystals of improved purity by Liquid Encapsulated Czochralski (LEC) pulling from pyrolytic boron nitride (PBN) crucibles and characterization of this material for direct ion implantation technology, is described. Three-inch diameter, 〈100〉-oriented GaAs crystals have been grown in a high pressure Melbourn crystal puller using 3 kg starting charges synthesized in-situ from 6/9s purity elemental gallium and arsenic. Undoped and Cr-doped LEC GaAs crystals pulled from PBN crucibles exhibit bulk resistivities in the 10⁷ and 10⁸ Ω cm range, respectively. High sensitivity secondary ion mass spectrometry (SIMS) demonstrates that GaAs crystals grown from PBN crucibles contain residual silicon concentrations in the mid 10¹⁴ cm^?3 range, compared to concentrations up to the 10¹⁶ cm^?3 range for growths in fused silica containers. The residual chromium content in undoped LEC grown GaAs crystals is below the SIMS detection limit for Cr (4 × 10¹⁴ cm^?3).The achievement of direct ion implanted channel layers of near-theoretical mobilities is further evidence of the improved purity of undoped, semi-insulating GaAs prepared by LEC/PBN crucible techniques. Direct implant FET channels with (1–1.5) × 10¹⁷ cm^?3 peak donor concentrations exhibit channel mobilities of 4,800–5,000 cm²/V sec in undoped, semi-insulating GaAs substrates, compared with mobilities ranging from 3,700 to 4,500 cm²/V sec for various Cr-doped GaAs substrates. The concentration of compensating acceptor impurities in semi-insulating GaAs/PBN substrates is estimated to be 1 × 10¹⁶ cm^?3 or less, and permits the implantation of 2 × 10¹⁶ cm^?3 channels which exhibit mobilities of 5,700 and 12,000 cm²/V sec at 298K and 77K, respectively.Discrete power FET's which exhibit 0.7 watts/mm output and 8 dB associated gain at 8 GHz have been fabricated using these directly implanted semi-insulating GaAs substrates.     

Passivation of carbon acceptors during growth of carbon-doped GaAs,InGaAs, and HBTs by MOCVD

Carbon dopedp-type GaAs and In_0.53Ga_0.47As epitaxial layers have been grown by low-pressure metalorganic chemical vapor deposition using CC1₄ as the carbon source. Low-temperature post-growth annealing resulted in a significant increase in the hole concentration for both GaAs and In_0.53Ga_0.47As, especially at high doping levels. The most heavily doped GaAs sample had a hole concentration of 3.6 × 10²⁰ cm⁻³ after a 5 minute anneal at ≈400° C in N₂, while the hole concentration in In_0.53Ga_0.47As reached 1.6 × 10¹⁹ cm⁻³ after annealing. This annealing behavior is attributed to hydrogen passivation of carbon acceptors. Post-growth cool-down in an AsH₃/H₂ ambient was found to be the most important factor affecting the degree of passivation for single, uncapped GaAs layers. No evidence of passivation is observed in the base region of InGaP/GaAs HBTs grown at ≈625° C. The effect ofn-type cap layers and cool-down sequence on passivation of C-doped InGaAs grown at ≈525° C shows that hydrogen can come from AsH₃, PH₃, or H₂, and can be incorporated during growth and during the post-growth cool-down. In the case of InP/InGaAs HBTs, significant passivation was found to occur in the C-doped base region.     

High purity and chrome-doped GaAs buffer layers grown by liquid phase epitaxy for mesfet application

High purity GaAs buffer layers of carrier concentration in the low (l-5)×l0^l4/cm³ range with 77K electron mobility over 100,000 cm²/V-sec and 300K mobility around 8000 cm?/ V-sec have been grown by liquid phase epitaxy on Cr-doped GaAs substrates using the graphite sliding boat method. The high purity has been achieved with systematic and concurrent long term bake-outs (24 hrs) of both LPE melt and substrate, both exposed to the H₂ ambient gas stream at 775?C, prior to epitaxial growth at 700?C. Substrate surface degradation was reduced by using Ga:GaAs etch melts that were undersaturated at 700?C by 5? to 40?C. Best buffer layer morphologies with regard to surface planarity were obtained using etch melts that were saturated by near 85% of weight of GaAs at 700°C. The importance of substrate preconditioning in order to achieve the low ( 1 -2)×l0¹⁴ was examined and found to be critical. Melt and substrate bake outs at 800?C, and use of a 40?C undersaturated etch melt prior to epitaxial growth at 800?C resulted in a p-type layer of carrier concentration, 1 .9×l0^l2/cm³ and resistivity 1×10⁵ ohm-cm. Chromium doping at 700?C resulted in buffer layers with sheet resistivities greater than 10 ohms/sq and low pinhole densities.     

Growth and characterization of (111)B InGaAs/GaAs multi-quantum well PIN diode structures

High quality piezoelectric strained InGaAs/GaAs multi-quantum well structures on (111)B GaAs substrates have been grown by solid-source molecular beam epitaxy in a PIN configuration. 10K photoluminescence (PL) shows narrow peaks with widths as low as 3 meV for a 25-period structure while room temperature (RT) PL shows several higher order peaks, normally forbidden, indicating breaking of inversion symmetry by the piezoelectric field. Furthermore, both the 10K PL peak position and the form of the RT PL spectra depend on the number of quantum wells within the intrinsic region, suggesting that the electric-field distribution is altered thereby. Diodes fabricated from these structures had sharp avalanche breakdown voltages (V_bd) and leakage currents as low as 8 × 10⁻⁶ A/cm² at 0.95 V_bd, indicating quality as high as in (100) devices. On leave from: Department de Ingeniera Electronica, Universidad Politecnica de Madrid, Madrid, Spain.     

Molecular beam epitaxy of AlGaAs/Zn(Mn)Se hybrid nanostructures with InAs/AlGaAs quantum dots near the heterovalent interface

Features of the growth of InAs quantum dots in an Al_0.35Ga_0.65As matrix by molecular beam epitaxy at different substrate temperatures, deposition rates, and amounts of deposited InAs are studied. The optimum conditions for growing an array of low-density (≤2 × 10¹⁰ cm^?2) small (height of no more than 4 nm) self-organized quantum dots are determined. The possibility of the formation of optically active InAs quantum dots emitting in the energy range 1.3–1.4 eV at a distance of no more than 10 nm from the coherent heterovalent GaAs/ZnSe interface is demonstrated. It is established that inserting an optically inactive 5-nm GaAs quantum well resonantly coupled with InAs quantum dots into the upper AlGaAs barrier layer enhances the photoluminescence efficiency of the quantum-dot array in hybrid heterostructures.     

MOVPE growth of InPSb/InAs heterostructures for mid-infrared emitters

We investigated the growth of InPSb on GaSb or InAs by low pressure (20 mbar) metalorganic vapor phase epitaxy (MOVPE). Trimethylindium, triethylantimony, and phosphine were used as starting materials. High resolution x-ray diffraction, photoluminescence at 10K, Hall measurements at 300 and 77K as well as scanning electron microscopy and scanning tunneling electron microscopy investigations were carried out to verify the layer properties. Lattice-matched InPSb layers on InAs substrate grown at 520°C show mirror-like surfaces and sharp x-ray peaks. N-type doping of InP_0.69Sb_0.31 was carried out with H₂S and p-type doping was achieved with DEZn. Maximum electron concentrations of 2×10¹⁹ cm⁻³ and hole concentrations exceeding 10¹⁸ cm⁻³ were obtained after annealing in N₂ ambient. The thermal stability of InPSb was studied during annealing experiments carried out at 500°C up to 30 min. The compositional integrity of the lattice proves to be stable and the InAs/InPSb interface can be improved. Multiple quantum well structures, pn-junction diodes and the two-dimensional electron gas at the InPSb/InAs/InPSb quantum wells were investigated to demonstrate the properties of the material.     

Heteroepitaxy of HgCdTe(112) infrared detector structures on Si(112) substrates by molecular-beam epitaxy

High-quality, single-crystal epitaxial films of CdTe(112)B and HgCdTe(112)B have been grown directly on Si(112) substrates without the need for GaAs interfacial layers. The CdTe and HgCdTe films have been characterized with optical microscopy, x-ray diffraction, wet chemical defect etching, and secondary ion mass spectrometry. HgCdTe/Si infrared detectors have also been fabricated and tested. The CdTe(112)B films are highly specular, twin-free, and have x-ray rocking curves as narrow as 72 arc-sec and near-surface etch pit density (EPD) of 2 × 10⁶ cm⁻² for 8 μm thick films. HgCdTe(112)B films deposited on Si substrates have x-ray rocking curve FWHM as low as 76 arc-sec and EPD of 3-22 × 10⁶ cm⁻². These MBE-grown epitaxial structures have been used to fabricate the first high-performance HgCdTe IR detectors grown directly on Si without use of an intermediate GaAs buffer layer. HgCdTe/Si infrared detectors have been fabricated with 40% quantum efficiency and R₀A = 1.64 × 10⁴ Ωm₂ (0 FOV) for devices with 7.8 μm cutoff wavelength at 78Kto demonstrate the capability of MBE for growth of large-area HgCdTe arrays on Si.     

Characterization of very high purity InAs grown using trimethylindium and tertiarybutylarsine

The growth of high purity InAs by metalorganic chemical vapor deposition is reported using tertiarybutylarsine and trimethylindiμm. Specular surfaces were obtained for bulk 5-10 μm thick InAs growth on GaAs substrates over a wide range of growth conditions by using a two-step growth method involving a low temperature nucleation layer of InAs. Structural characterization was performed using atomic force microscopy and x-ray diffractometry. The transport data are complicated by a competition between bulk conduction and conduction due to a surface accumulation layer with roughly 2–4 × 10¹² cm⁻² carriers. This is clearly demonstrated by the temperature dependent Hall data. Average Hall mobilities as high as 1.2 x 10⁵ cm²/Vs at 50K are observed in a 10 μm sample grown at 540°C. Field-dependent Hall measurements indicate that the fitted bulk mobility is much higher for this sample, approximately 1.8 × 10⁵ cm²/Vs. Samples grown on InAs substrates were measured using high resolution Fourier transform photoluminescence spectroscopy and reveal new excitonic and impurity band emissions in InAs including acceptor bound exciton “two hole transitions.” Two distinct shallow acceptor species of unknown chemical identity have been observed.     

Tertiarybutylarsine for Metalorganic Chemical Vapor Deposition Growth of High Purity, High Uniformity Films

We have performed an extensive study of GaAs, Al_0.22Ga_0.78As, and In_0.16Ga_0.84As grown using tertiarybutylarsine (TBA) in an ultra-high purity metalorganic chemical vapor deposition multi-wafer reactor. Key results include: high purity TBA AlGaAs layers with the lowest p-type carrier concentrations (4 × 10¹⁴ cm⁻³) reported to date; 4K photoluminescence bound exciton linewidths as narrow as 4.3 meV; C, O. Si, and S concentrations below the secondary ion mass spectrometry detection limit; and InGaAs/GaAs quantum wells with 20K PL linewidths as narrow as 3.5 meV. We also observe a strong dependence of growth rates and doping efficiency on group-V partial pressure, possibly due to a competition between excess group-V species and group-Ill or Si species for group-Ill surface sites. Finally, we demonstrate record uniformity using TBA with an AlGaAs thickness variation of only ±1.4% across a 4 inch wafer.     

Oxygen incorporation,photoluminescence, and laser performance of AlGaAs grown by organometallic vapor phase epitaxy

Photoluminescence (PL) of separate confinement heterostructure, single quantum well (SCH-SQW) laser material provides a quantitative evaluation of the quality of AIGaAs grown by organometallic vapor phase epitaxy. There is a good correlation between the oxygen level in the quantum well confining layers measured by secondary ion mass spectroscopy, quantum well PL efficiency, and laser threshold current. When oxygen was reduced from 2.0 × 10¹⁸ cm⁻³ to 1.5 × 10¹⁷ cm^-3, the PL intensity increased by a factor of 12, and the threshold current density was improved from 1300 to 240 A/cm² for a 100 × 600 μm device. Oxygen levels were decreased by using a higher growth rate, shorter interface pause time, higher V/III ratio, and an arsine purifier.     

Effect of fluorine on the electrical properties of anodic oxide/InAs(111)A interface

The electrical properties of metal-insulator-semiconductor structures based on InAs(111)A with thin anodic insulator layers of various thicknesses (7–20 nm) are investigated. It is established that the oxidation of InAs in a fluorinated acid electrolyte results in decreasing density of surface states and fixed charge in the anodic layer to values of < 2 × 10¹⁰ cm^?2 eV^?1 and ～3 × 10¹¹ cm^?2, respectively. Comparison of the electrical parameters with the chemical composition of the layers shows that an improvement in the parameters of the fluorinated anodic oxide/InAs(111)A interface is caused by the substitution of oxygen atoms for fluorine in the anode layers with the formation of indium and arsenic oxifluorides and In-F bonds on the InAs surface.     

Liquid phase epitaxial growth and characterization of high purity lattice matched GaxIn1-xAs ON <111>B InP

High purity Ga_xIn_1-x As has been grown lattice matched on <111>B InP by liquid phase epitaxy. Silicon, the residual impurity, is purged from the melt by long time baking in a hydrogen atmosphere with slight ambient water vapor concentration. Epitaxial layers with a net electron concentration as low as 3.5 × 10¹⁴ cm^-3 and a liquid nitrogen mobility of 70,000 cm²/Vsec have been grown. The room temperature mobility is shown to be significantly higher than GaAs over a wide range of net electron concentrations useful for device applications, with the highest value of μ₃₀₀ = 13,800 cm²/Vsec on a sample with n = 1.9 × I0¹⁵ cm_-3