Influence of growth conditions on the formation and luminescence properties of InGaAs quantum dots in a Si matrix

The influence of the growth conditions during molecular-beam epitaxy and of the degree of lattice mismatch between the epilayer and the substrate on the formation of InGaAs islands on a Si(100) surface is studied. An increase in lattice mismatch (the InAs mole fraction) leads to an increase in the critical thickness corresponding to the onset of island growth, in contrast to the formation of InGaAs islands on GaAs(100). An increase in the deposition temperature also increases the critical thickness, whereas an increase in the arsenic pressure has the opposite effect. Structures containing an array of InGaAs islands in a Si matrix display a luminescence line in the range 1.2–1.3 μm, depending on the mole fraction of InAs. Fiz. Tekh. Poluprovodn. 33, 194–197 (February 1999)     

Process characterization and evaluation of hydride VPE grown Ga x In1−x As using a Ga/In alloy source

A novel, simplified hydride vapor phase epitaxy (VPE) method based on the utilization of Ga/In alloys as the group III source was studied for deposition of Ga_xIn_1-xAs. The effects of a wide range of experimental variables (i.e., inlet mole fractions of HC1 and AsH₃, deposition temperature, gas velocity, Ga/ln alloy composition, and reactor geometry) on the ternary composition and growth rate were investigated. The growth rate of Ga _x In₁₋ xAs was found to increase with increasing deposition temperature and exhibited a maximum with inlet HC1 mole fraction. The growth rate increases slightly with inlet AsH₃ mole fraction and is independent of gas velocity. The Ga composition of the deposited film increased with increasing inlet HC1 mole fraction and gas velocity. Increased In concentrations were observed with increases in inlet AsH₃ mole fraction and deposition temperatures. Layers of Ga_0.47In_0.53As lattice matched to InP were successfully grown from alloys containing 5 to 8 at.% Ga. These layers were used to produce state-of-the-artp- i- n photodetectors having the following characteristics: dark current,I _d(- 5 V) = 10-20 nA; responsivity,R = 0.84-0.86 A/W; capacitance,C = 0.88–0.92 pF; breakdown voltage,V _b > 40 V. This study demonstrated for the first time that a simplified hydride VPE process with a Ga/ln alloy source is capable of producing device quality epitaxial layers.     

The growth of GaAs,AIGaAs, InP and InGaAs by chemical beam epitaxy using group III and V alkyls

The growth kinetics of chemical beam epitaxy (CBE) were investigated with the growth of GaAs, AIGaAs, InP, and InGaAs. Results obtained with epilayers grown by using trimethylarsine (TMAs) and triethylphosphine (TEP) instead of arsine (AsH3) and phosphine (PH₃) were reviewed with some additional results. The CBE grown epilayers have similar optical quality to those grown by molecular beam epitaxy (MBE). Superlattices of GaAs/AlGaAs with abrupt interfaces have been prepared. Since trimethylindium (TMIn) and triethylgallium (TEGa) used in the growth of InGaAs emerged as a single mixed beam, spatial composition uniformity was automatically achieved without the need of substrate rotation in the InGaAs epilayers grown. Lattice-mismatch Δα/α< 1 x 10^-3 have been reproducibly obtained. For epilayers grown with high purity TMAs source, room-temperature electron mobility as high as 9000 cm²/V sec and concentrations of ˜7 x 10¹⁵ cm^-3 were produced. In general, the electron mobilities were as good as those obtained from low-pressure metalorganic chemical vapor deposition. (MO-CVD). Unlike MBE, since the In and Ga were derived by the pyrolysis of TMIn and TEGa molecules at the heated substrate surface, respectively, oval defects observed in MBE grown epilayers due to Ga splitting from Ga melt were not present in CBE grown epilayers. This is important for integrated circuit applications. Unlike MO-CVD, the beam nature of CBE allows for selective area growth of epilayers with well-defined smooth edges using mask shadowing techniques. Typically, growth rates of 2-5μm/h for InP, 2-6μm/h for GaAs and AIGaAs, and 2-5μm/h for InGaAs were used.     

Structural properties of ZnSy Se1−yZnSe/GaAs (001) heterostructures grown by photoassisted metalorganic vapor phase epitaxy

ZnS_ySe_1−yZnSe/GaAs (001) heterostructures have been grown by photoassisted metalorganic vapor phase epitaxy, using the sources dimethylzinc, dimethylselenium, diethylsulfur, and irradiation by a Hg arc lamp. The solid phase composition vs gas phase composition characteristics have been determined for ZnSy_ySe_1−y grown with different mole fractions of dimethylselenium and different temperatures. Although the growth is not mass-transport controlled with respect to the column VI precursors, the solid phase composition vs gas phase composition characteristics are sufficiently gradual so that good compositional control and lattice matching to GaAs substrates can be readily achieved by photoassisted growth in the temperature range 360°C ≤ T ≤ 400°C. ZnSe/GaAs (001) single heterostructures were grown by a two-step process with ZnSe thicknesses in the range from 54 nm to 776 nm. Based on 004 x-ray rocking curve full width at half maximums (FWHMs), we have determined that the critical layer thickness is h_c ≤200 nm. Using the classical method involving strain, lattice relaxation is undetectable in layers thinner than 270 nm for the growth conditions used here. Therefore, the rocking curve FWHM is a more sensitive indicator of lattice relaxation than the residual strain. For ZnS_ySe_1−y layers grown on ZnSe buffers at 400°C, the measured dislocation density-thickness product Dh increases monotonically with the room temperature mismatch. Lower values of the Dh product are obtained for epitaxy on 135 nm buffers compared to the case of 270 nm buffers. This difference is due to the fact that the 135 nm ZnSe buffers are pseudomorphic as deposited. For ZnS_ySe_1−y layers grown on 135 nm ZnSe buffers at 360°C, the minimum dislocation density corresponds approximately to room-temperature lattice matching (y ∼ 5.9%), rather than growth temperature lattice matching (y ∼ 7.6%). Epitaxial layers with lower dislocation densities demonstrated superior optical quality, as judged by the near-band edge/deep level emission peak intensity ratio and the near band edge absolute peak intensity from 300K photoluminescence measurements.     

The equilibrium constant for the reaction of ZnO + H2 and the chemical vapor transport of zno via the Zn + H2O reaction

Using a gas transpiration method, the equilibrium constant for the reaction ZnO(s) + H₂(v)⇄ Zn(v) + H₂O(v) was determined directly in the temperature interval 592–950°C. The data are described by the equation log₁₀K = [-11.794 × 10³/T] + 8.040 with ΔH° = 53.97 Kcal/mole and ΔS° = 36.79 e.u. Based on this Information, vapor-solid gas concentration curves useful for defining conditions for the chemical vapor transport of ZnO via the reverse of the above reaction have been computer calculated.     

The growth of high quality InP/InGaAs/InGaAsP interfaces by CBE for SCH multi-quantum well lasers

Bulk InGaAsP and heterointerfaces of InP/InGaAs and InGaAsP/InGaAs have been grown by chemical beam epitaxy for use in multi-quantum well separate confinement heterostructure lasers. InGaAsP has been successfully grown for λ=1.1, 1.2 and 1.4 μm. The TMI and TEG incorporation coefficients have strong dependencies on substrate temperature and also charge as the InGaAsP composition tends towards InP. InP/InGaAs and InGaAsP/InGaAs quantum wells have been grown to determine the optimum gas switching sequence to minimize the measured photoluminescence FWHM. InGaAs quantum wells as narrow as 0.6 nm have been grown with 7K FWHM of 12.3 meV. Lattice matched MQW-SCH lasers were grown using different interface switching sequences with the best laser having a threshold current density of 792A/cm² for an 800 × 90 μm broad area device.     

Spaser operation in the presence of external optical field

The operation of surface plasmon amplifier by stimulated emission of radiation (spaser) in the presence of external optical field is analyzed. The range of external field amplitude E and mismatch Δ of the external field frequency and the spaser generation frequency (Arnold tongue) E > E _synchr(Δ) in which the spaser works at the external field frequency is determined. The analytical and numerical calculations at the given mismatch Δ yield three ranges: E < E _synchr(Δ) (the spaser exhibits stochastic regime and point (Δ, E) is outside the Arnold tongue), E _synchr(Δ) < E < E _L (Δ) (transient range where the spaser polarization weakly depends on the field amplitude and is mainly determined by the pump level), and E > E _L (the spaser generation is suppressed and the spaser polarization is equal to the polarization of nanoparticle in the presence of external field).     

Influence of mismatch of the lattice parameters on the structural, optical, and transport properties of InGaAs layers grown by molecular beam epitaxy on InP(100) substrates

The influence of mismatch stress on the structural, optical, and transport properties of thick InGaAs layers grown on InP(100) substrates by molecular-beam epitaxy is investigated. It is found that layers having tensile stress can be grown with a greater mismatch than compressively stressed layers before plastic relaxation sets in. The critical mismatch for thick InGaAs layers is not described with sufficient accuracy by either the mechanical equilibrium model or the energy balance model. The range of mismatches required to obtain high carrier mobilities and high radiative recombination efficiencies in InGaAs layers grown on InP substrates is much narrower than the pseudomorphic growth range. The maximum mobilities and minimum widths of the photoluminescence peak are attained in layers matched with the substrate in terms of the lattice parameter and also in slightly gallium-enriched layers. The compositional dependence of the width of the band gap is investigated with allowance for the influence of stress. Fiz. Tekh. Poluprovodn. 31, 19–22 (January 1997)     

Structure and properties of InGaAs layers grown by low-temperature molecular-beam epitaxy

This paper describes studies of InGaAs layers grown by molecular-beam epitaxy on InP (100) substrates at temperatures of 150–480 °C using various arsenic fluxes. It was found that lowering the epitaxy temperature leads to changes in the growth surface, trapping of excess arsenic, and an increased lattice parameter of the epitaxial layer. When these lowtemperature (LT) grown samples are annealed, the lattice parameter relaxes and excess arsenic clusters form in the InGaAs matrix. For samples grown at 150 °C and annealed at 500 °C, the concentration of these clusters was ∼8×10¹⁶ cm⁻³, with an average cluster size of ∼5 nm. Assuming that all the excess arsenic is initially trapped in the form of antisite defects, the magnitude of the LT-grown InGaAs lattice parameter relaxation caused by annealing implies an excess arsenic concentration (N _As−N _Ga−N _In)/(N _As+N _Ga+N _In)=0.4 at.%. For layers of InGaAs grown at 150 °C, a high concentration of free electrons (∼1×10¹⁷ cm⁻³) is characteristic. Annealing such layers at 500 °C decreases the concentration of electrons to ∼1×10¹⁷ cm⁻³. The results obtained here indicate that this change in the free-electron concentration correlates qualitatively with the change in excess arsenic concentration in the layers. Fiz. Tekh. Poluprovodn. 33, 900–906 (August 1999)     

Barrier width dependence of leakage currents in InGaAs/ GaAs multiple quantum well P-I-N diodes

A range of InGaAs/GaAs strained layer multiple quantum well pin diode structures with different barrier dimensions has been grown and characterized. High quality low leakage structures (< 2 × 10⁻⁴ A/cm² @ 0.9 V _BD ) with a high degree of strain (∼2%) have been produced. An important factor affecting the leakage for a fixed well composition and dimension is found to be the barrier width.     

Flexibility of p–n Junction Formation from SWIR to LWIR Using MBE-Grown Hg(1–x)CdxTe on Si Substrates

In this paper, we show the versatility of using molecular-beam epitaxy (MBE) for the growth of the mercury cadmium telluride (HgCdTe) system. Abrupt composition profiles, changes in doping levels or switching doping types are easily performed. It is shown that high-quality material is achieved with Hg_(1–x)Cd _x Te grown by MBE from a cadmium mole fraction of x = 0.15 to x = 0.72. Doping elements incorporation as low as 10¹⁵ cm⁻³ for both n-type and p-type material as well as high incorporation levels >10¹⁸ cm⁻³ for both carrier types were achieved. X-ray curves, secondary-ion mass spectrometry (SIMS) data, Hall data, the influence of doping incorporation with cadmium content and growth rate, etch pit density (EPD), composition uniformity determined from Fourier-transform infrared (FTIR) transmission spectro- scopy, and surface defect maps from low to high x values are presented to illustrate the versatility and quality of HgCdTe material grown by MBE. All data presented in this work are from layers grown on silicon (112) substrate.     

Internal strain and dislocations in Ga1−xAs crystals grown by liquid phase epitaxy/electroepitaxy

Strain relaxed, low dislocation density In_xGa_1−xAs crystals, 0 < x <0.2, have been successfully grown by liquid phase electroepitaxy on the GaAs substrate, despite the crystal/substrate lattice mismatch. Residual strain in these novel substrates is below 10⁻⁴, at least an order of magnitude lower than in the molecular beam epitaxially (MBE) or metalorganic chemical vapor deposition-grown ternary buffer layers of similar composition. Threading dislocation density induced by both the crystal/substrate lattice mismatch and unavoidable composition variations has been reduced from the low 10⁶ cm⁻² range, while growing directly on GaAs, to the mid 10⁴ cm^-2 by employing both the MBE grown ternary buffer layer and selective lateral overgrowth of an SiO₂ mask which, prior to the crystal growth, was deposited on the buffer layer and patterned by photolithography with 10 μm wide, oxide free seeding windows. The full width at half maximum of the rocking curves measured for In_xGa_1−xAs crystals grown by liquid phase epitaxy/electroepitaxy on patterned, closely lattice matched buffer layers was in the 20–23 arc s range. Further reduction of the dislocation density and a more uniform dislocation distribution is expected by modifying the initial growth conditions, improving substrate preparation, and optimizing the seeding window geometry.     

InP-based InxGa1-xAs metamorphic buffers with different mismatch grading rates

Linearly graded In_xGa_1-xAs metamorphic buffers with different mismatch grading rates were grown on InP substrate by gas source molecular beam epitaxy.Room temperature photoluminescence spectra show that the sample with lower mismatch grading rate in the buffer has stronger photoluminescence signal,indicating the improved optical property.Atomic force microscope images show that the lower mismatch grading rate in the buffer leads to a slightly rougher surface.The relaxation procedure with two steps in the buffer layers has been observed by X-ray diffraction reciprocal space mapping.The measurements of X-ray diffraction also reveal that the lower mismatch grading rate in the buffer is beneficial for the lattice relaxation and release of residual strain.To further increase the relaxation degree,a lower mismatch grading rate and composition "overshoot" are suggested.     

Growth and properties of Hg1-xCdxTe on GaAs,with x − 0.27

The organometallic vapor phase epitaxy of HgCdTe onto (100)2°-(110) GaAs substrates is described in this paper. A buffer layer of CdTe has been grown prior to the growth of HgCdTe, to take up the large lattice mismatch with the GaAs. Considerations for the thickness of this buffer layer are outlined, and it is shown by quantitative Secondary Ion Mass Spectroscopy that there is negligible diffusion of gallium from the GaAs substrate for the growth conditions described. Hall effect measurements give mobilities comparable to those reported for bulk grown crystals. An extrinsicn-type carrier concentration of 2 × 10¹⁶/cm³ is obtained, and is mainly due to residual impurities in the starting chemicals. The alloy composition has been determined at 298 K by Fourier transform infrared transmission (FTIR) spectrometry; this is found to be extremely uniform over a 15 × 7 mm area, as evidenced by an overlapping of FTIR plots taken over this area. HgCdTe layers have been grown on buffer layers varying in thickness from 0.1 to 1.9μm. It is found that a buffer thickness of about 1.9μm or larger is required to obtain high quality HgCdTe, both in terms of the electrical characteristics (mobility and carrier concentration) and the infrared transmission curves (peak transmission).     

On the carrier profiling of GaAsSb/GaAs heterostructures

Carrier profiles of MBE grown Ga(As,Sb)/GaAs heterostructures were studied. In low Sb content samples of Ga(As,Sb)/GaAs grown by MBE the experimentally measured carrier profiles exhibit double dips in concentration, whereas a single large dip is ob-tained for higher Sb content with larger lattice-mismatched samples. The capacitance voltage(C-V) carrier profile of a Schottky barriern- N heterojunction of Au/n-GaAsSb/N-GaAs has been modeled and double dips occur when nonuniform doping is present which may explain the experimentally observed double dips in a GaAs_0.95Sb_0.05/GaAs specimen. For large lattice mismatch and therefore large heterointerface charge density in the model, the accumulation peak due to ΔE_c is shown to be overwhelmed by a pro-nounced single dip as observed in higher Sb content samples such as GaAs_0.91Sb_0.09/ GaAs and GaAs/GaAs_0.9Sb_0.1.     

Influence of elastic stresses on the character of epitaxial crystallization of (Hg, Mn)Te

Available experimental data on the composition and conditions for crystallization of semiconductor Hg_1−z Mn_zTe solid-state solutions epitaxially grown on Cd(Zn)Te substrates reveal a number of peculiarities, which indicate that the substrate strongly affects the character of crystallization of the solid phase. In this paper we discuss data on liquid-phase epitaxy of Hg_1−z Mn_zTe which suggest the possibility that elastic stresses caused by the mismatch between the crystal lattice parameters of the substrate and the epitaxial layer can influence the composition and conditions for crystallization of these layers. An important tool in our investigation is a thermodynamic analysis of the metastable equilibrium between the stressed solid phase and the supersaturated solution of components. Fiz. Tekh. Poluprovodn. 31, 342–346 (March 1997)     

Comparison of spatial compositional uniformity and dislocation density for organometallic vapor phase epitaxial Hg1−x CdxTe grown by the direct alloy and interdiffused growth processes

Etch pit density and spatial compositional uniformity data are presented for organometallic vapor phase epitaxial Hg_1−x Cd_x Te grown by the direct alloy and interdiffused growth methods. For alloy growth, composition variation is as low as Δx=0.004 and 0.02 over 2- and 3-in diam areas, respectively; while for growth on CdZnTe substrates, etch pit density values lower than 2×10⁵ cm⁻² have been achieved. For interdiffused growth on CdZnTe, etch pit density values lower than 5×10⁵ cm⁻² have been obtained, while the composition variation is usually Δx≤0.004 and 0.014 over 2- and 3-in diam areas, respectively. Data demonstrate that the choice of particular CdZnTe substrate strongly affects the subsequent etch pit density measured in the layer. Reasonably uniform n-type doping over 3-in diam area using the source triethylgallium is also reported for both growth methods.     

Effect of AlInGaN barrier layers with various TMGa flows on optoelectronic characteristics of near UV light-emitting diodes grown by atmospheric pressure metalorganic vapor phase epitaxy

Near ultraviolet light-emitting diodes (LEDs) with quaternary AlInGaN quantum barriers (QBs) are grown by atmospheric pressure metalorganic vapor phase epitaxy. The indium mole fraction of AlInGaN QB could be enhanced as we increased the TMG flow rate. Both the wavelength shift in EL spectra and forward voltage at 20 mA current injection were reduced by using AlInGaN QB. Under 100 mA current injection, the LED output power with Al_0.089In_0.035Ga_0.876N QB can be enhanced by 15.9%, compared to LED with GaN QB. It should be attributed to a reduction of lattice mismatch induced polarization mismatch in the active layer.     

Suppression of strain-induced cross-hatch on molecular beam epitaxy (211)B HgCdTe

Because the performance of HgCdTe-based photodiodes can be significantly degraded by the presence of dislocations, we have systematically investigated and suppressed lattice-mismatch-induced cross-hatch formation and the associated generation of dislocations in (211)B HgCdTe/CdZnTe. A series of HgCdTe epilayers were deposited simultaneously on pairs of substrates with differing ZnTe mole fractions. Epilayers’ CdTe mole fraction and substrates’ ZnTe mole fractions were measured using optical-transmission spectra. Lattice mismatch and residual strain were estimated from room-temperature, x-ray diffraction, and double-crystal rocking-curve measurements (DCRC). It was found that cross-hatch patterns were suppressed in epilayers deposited on nearly lattice-matched substrates (|Δa/a_sub|<0.02%). Such epilayers exhibited excellent crystalline quality as revealed by defect-decoration etching (etch-pit density (EPD)<10⁵ cm⁻²) and x-ray diffraction (full-width at half-maximum (FWHM) ∼10 arcsec). In addition to determining the upper limits of lattice mismatch needed to eliminate cross-hatch, we investigated the use of reticulated substrates as a means to suppress cross-hatch. We found that growth on reticulated mesa structures (<100 μm) with edges parallel to [01-1] resulted in epilayers with substantially reduced cross-hatch-line densities despite large lattice mismatch (Δa/a_sub <0.04%). The use of reticulated substrates could suppress cross-hatch because of lateral-alloy variation in large substrates and complex multistack epilayers (e.g., multicolor detectors).     

Aluminum Gallium Nitride Alloys Grown via Metalorganic Vapor-Phase Epitaxy Using a Digital Growth Technique

This work investigates the use of a digital growth technique as a viable method for achieving high-quality aluminum gallium nitride (Al _x Ga_1−x N) films via metalorganic vapor-phase epitaxy. Digital alloys are superlattice structures with period thicknesses of a few monolayers. Alloys with an AlN mole fraction ranging from 0.1 to 0.9 were grown by adjusting the thickness of the AlN layer in the superlattice. High-resolution x-ray diffraction was used to determine the superlattice period and c-lattice parameter of the structure, while reciprocal-space mapping was used to determine the a-lattice parameter and evaluate growth coherency. A comparison of the measured lattice parameter with both the nominal value and also the underlying buffer layer is discussed.