Gas-source Molecular Beam Epitaxy Growth Research Articles

Gas source molecular-beam epitaxial growth of TlInGaAsN double quantum well light emitting diode structures and thallium incorporation characteristics

TlInGaAsN/GaAs double quantum well (DQW) structures were grown on GaAs (1 0 0) substrates by gas source molecular-beam epitaxy. It has been found that high Tl flux is needed for the incorporation of Tl into the films. Reduction in the temperature variation of electroluminescence (EL) peak energy has been observed by the addition of Tl into quantum well (QW) layers; −0.62 meV/K for the InGaAsN/GaAs DQW light emitting diodes (LEDs) and −0.53 meV/K for the TlInGaAsN/GaAs DQW LEDs. By replacing GaAs barrier layers with TlGaAs barrier layers, further reduction could be obtained; −0.35 meV/K for TlInGaAsN/TlGaAs DQW LEDs. SIMS measurements indicated that this improvement is caused by the increased incorporation of Tl into the QW layers.

Studies of ammonia dissociation during the gas source molecular-beam epitaxial growth of III nitrides

This article presents a method for the observation of ammonia dissociation during the gas source molecular-beam epitaxial (MBE) growth of group III nitrides. The mass spectrometer, present in most molecular beam epitaxy machines, is used to detect H2, a biproduct of ammonia dissociation. A direct line of sight, from the mass spectrometer to the substrate, is not required. The technique is used to examine several aspects of the MBE growth of AlN, GaN, and GaInN. Aluminum is approximately six times more efficient in causing ammonia dissociation than is gallium, which in turn is similarly more efficient than indium. During the growth of GaInN, transient effects in ammonia dissociation are observed following indium shutter actuations, indicative of indium surface accumulation.

Gas-source molecular-beam epitaxial growth of Ga(In)NP on GaP(100) substrates for yellow-amber light-emitting devices

In this article we describe growth and characterization of Ga(In)NP on GaP(100) substrates. Increasing the nitrogen composition in the GaNP bulk layers from 0.6% to 1.7% shifts the light emission color from yellow-amber to red. The optimal substrate temperature window of 500–520°C for GaNP layers growth was determined from analysis of both structural and optical properties. Incorporation of up to 20% indium into a GaN0.008P0.992 quantum well leads to a redshift of PL peak position and increasing of the photoluminescence intensity by a factor of 12. Ga(In)NP grown on transparent GaP substrates is considered to be an attractive material system for amber-red light-emitting devices.

Low threshold distribution feedback quantum cascade lasers at 7.6 μm grown by gas source molecular beam epitaxy

We have demonstrated the first Gas source molecular beam epitaxy (GSMBE) grown distributed feedback quantum cascade laser (DFB QC-laser) laser with low threshold current density operation at 7.6 μm. High quality DFB QC-laser heterostructures were grown by an one step GSMBE growth procedure. The first-order grating was defined by a holographic technology. A tunable single mode DFB QC-laser operation in pulsed mode with a low threshold current density of 574 A/cm 2 and a peak optical power of 50 mW at 70 K and 7.6 μm have been obtained. The side mode suppression ratio and the maximum single mode wavelength tuning range by changing their heat sink temperature are 23 dB and 20 nm, respectively.

High-performance enhancement-mode pseudomorphic InGaP/InGaAs/GaAs HEMT structures by gas source molecular beam epitaxy

Abstract Enhancement-mode (E-mode) operation In 0.49 Ga 0.51 P/In 0.2 Ga 0.8 As/GaAs PHEMTs were designed for high performance and were successfully grown by gas source molecular beam epitaxy (GSMBE). An optimized GSMBE growth process based on the memory effect studied has been applied to precisely control the InGaP/InGaAs and InGaP/GaAs interface quality and composition. The lattice mismatch of 10 −4 and composition uniformity of better than ±0.2% for 3″ diameter InGaP/GaAs layers were obtained. E-mode operation InGaP/InGaAs PHEMTs and related low-noise amplifier (LNA) circuits were obtained. The E-mode PHEMT had a threshold voltage near 0 V and the LNA can operate under a single-voltage supply of 1.5–3.0 V and at 2.5 GHz with a gain of over 20 dB and a noise figure ( N f ) of 3.43 dB.

Gas source molecular-beam epitaxy growth of GaN/GaP superlattices and GaN layers on GaP(1 1 1)A substrates

GaN/GaP short-period superlattices were grown on GaP(1 1 1)A substrates by gas source molecular-beam epitaxy. Despite the large lattice-mismatch between GaN and GaP, reflection high-energy electron diffraction patterns showed the quick switch from GaN (GaP) streaks to GaP (GaN) streaks just after the corresponding switch of the growth. This indicates two-dimensional layer-by-layer growth resulting from the relaxation of lattice strain at the initial stage of the hetero-epitaxy. This phenomenon is considered to be due to the use of (1 1 1)A-oriented substrates. Bulk GaN layers were also grown on GaP(1 1 1)A substrates and the flat-surface GaN layers were obtained because of the two-dimensional layer-by-layer growth starting from the interface between GaN and GaP (1 1 1)A substrates. Strong near-band-edge photoluminescence with very weak deep-level emission was observed. GaP(1 1 1)A substrate is considered to be promising for the growth of GaN.

The effect of coincident atomic hydrogen on the gas-source molecular beam epitaxial growth of silicon from disilane

The interaction of atomic hydrogen with both the clean Si(1 0 0) surface, and this same surface under conditions leading to steady-state epitaxial growth of Si from the reaction of disilane, Si 2H 6, has been examined. Reflectance anisotropy spectroscopy has been employed to measure the hydrogen adatom coverage on vicinal Si(1 0 0) surfaces as a function of atomic hydrogen exposure at differing substrate temperatures and differing atomic hydrogen fluxes. This set of experimental data can be fit well by a “hot-precursor” model that includes the elementary steps of adsorption, abstraction, migration, and desorption of atomic hydrogen, and where we account explicitly for adsorption site occupancy. Reflection high-energy electron diffraction has been used to quantify the effect of atomic hydrogen on the gas-source molecular beam epitaxial growth of Si from Si 2H 6. We observe suppression of the epitaxial growth rate by atomic hydrogen under a variety of reaction conditions. This set of data are described well by a model that combines rate expressions for the dissociative adsorption of Si 2H 6, the adsorption of atomic hydrogen, and the recombinative desorption of molecular hydrogen from the Si(1 0 0) surface.

Optical second harmonic generation studies of epitaxial growth of Si and SiGe

Optical second harmonic generation (SHG) from Si surfaces has the advantage of surface sensitivity and can be applied in-situ during epitaxial growth process such as gas source molecular beam epitaxy (GSMBE) or chemical vapour depositions (CVD). This enables a number of processes occurring on the surface during epitaxial growth to be investigated in real time. Two processes are of particular interest in the epitxial growth of Si and SiGe structures: (1) oscillatory processes on the surface due to layer-by-layer growth for growth rate measurements and (2) surface segregation of Ge during formation of Si/SiGe heterojunctions. In this paper, we report on the oscillatory SHG response from the Si(0 0 1) surface during homo-epitaxy of Si and variations of SHG response across the SiGe/Si heterojunction during GSMBE growth. The oscillatory response is attributed to the domain coverage variation during layer-by-layer growth analogous to the origin of reflectance anisotropy oscillations. The changes in SHG during formation of SiGe/Si heterojunction is attributed to the gradual variation of surface Ge concentration due to segregation of Ge. The contribution from buried interfaces is shown to be negligible at the photon energy used.

Gas-source MBE growth of Tl-based III–V semiconductors and their Raman scattering characterization

Ternary TlGaP and TlGaAs alloys, which are important constituent quaternary alloys of Tl x In 1− x− y Ga y P and Tl x In 1− x− y Ga y As as new III–V compound semiconductors for long wavelength optical devices as well as temperature-insensitive wavelength laser diodes, are successfully grown by gas-source molecular beam epitaxy (MBE). Optical phonon modes of TlGaP and TlGaAs ternary alloys are investigated, for the first time, by Raman scattering measurement. The Raman spectra of TlGaP with larger Tl composition on GaAs substrate consist of four separate bands in the optical frequency range, GaP-like LO 393 cm −1, GaP-like TO 357 cm −1, TlP-like LO 346 cm −1 and TlP-like TO 307 cm −1, respectively. The GaAs-like phonon modes for TlGaAs on InP substrate are also observed. The results show an agreement between the Raman scattering measurements and X-ray diffraction experiments.

Characterization of gas-source molecular beam epitaxial growth of strain-compensated Si 1− x− yGe xC y/Si(0 0 1) heterostructure

Strain-compensated SiGeC ternary alloys have been successfully grown on Si(0 0 1) substrate by gas-source molecular beam epitaxy. Si 2H 6 and GeH 4 are used as Si and Ge sources, respectively, while CH 6Ge (monomethylgermane: CH 3GeH 3, MMGe) is employed as the C source. Compressive strain in the SiGe/Si system is reduced by adding MMGe, which works not only as a C source but also as a Ge source. The magnitude of strain is evaluated by MeV-ion channeling. An almost strain-compensated Si 0.794Ge 0.19C 0.016/Si(0 0 1) heterostructure is grown at 550°C with good uniformity and a flat surface.

Study of Reflection High-Energy Electron Diffraction Oscillation for Optimization of Tertiarybutylphosphine-Based Molecular Beam Epitaxial Growth of In0.48Ga0.52P on GaAs

A detailed study of reflection high-energy electron diffraction (RHEED) oscillation was made for the tertiarybutylphosphine (TBP)-based gas-source molecular beam epitaxial (GSMBE) growth of In1-xGaxP on GaAs in order to obtain lattice-matched layers (x=0.52) with high electrical qualities. For growth of InGaP on conventional As-rich c(4×4) GaAs surfaces obtained by cooling under As4 flux irradiation after GaAs growth, no RHEED oscillation was observed. On the other hand, by growing InGaP layer on As-stabilized (2×4) GaAs surfaces obtained by exposure to low As4 pressures, clear and persistent RHEED oscillations were successfully observed for the first time. Growth under a sufficient TBP flow rate with careful adjustment of the substrate temperature within a narrow range was found to be important for realizing stable layer-by-layer growth of InGaP layer and for obtaining high-quality layers. The optimal InGaP layers achieved minimum full-width at half maximum (FWHM) values of X-ray diffraction (XRD) and photoluminescence (PL) peaks of 18 s and 15.5 meV, respectively. Nondoped layers grown under the optimal conditions realized high electron mobility values of 3,300 cm2/Vs at 300 K and 21,000 cm2/Vs at 77 K with low residual carrier concentration values of 5×1014–5×1015 cm-3. These are the best values reported so far for InGaP layers grown by GSMBE using TBP and are comparable to the best values reported so far for InGaP layers grown by other methods.

Gas-Source Molecular Beam Epitaxial Growth of In1-xGaxP on GaAs Using Tertiarybutylphosphine

A systematic study of growth was made for gas-source molecular beam epitaxial (GSMBE) growth of In1-xGaxP using tertiarybutylphosphine (TBP), in order to establish the conditions required to grow high-quality In1-xGaxP layers on GaAs(100) substrates. To clarify the effect of the P2 supply rate on growth, a special effort was made to increase the P2 supply by modifying the structure of the conventional cracking cell. The alloy composition and growth rate depended strongly on the type of cracking cell, growth temperature and TBP flow rate. The growth was group-III-limited at low growth temperatures, but became limited by thermal desorption of phosphorus at higher temperatures. The use of a high-efficiency cracking cell was found to be important for suppressing phosphorous evaporation and growing high-quality InGaP layers with controlled thickness and alloy compositions. Optimized growth led to an excellent photoluminescence (PL) property with a narrow peak width of 15.5 meV at 77 K and 38 meV at 300 K. These are comparable to the best data reported so far for InGaP layers grown by any method.

The effect of Al on Ga desorption during gas source-molecular beam epitaxial growth of AlGaN

In this letter, we report on the impact aluminum has on gallium desorption kinetics in AlGaN alloys grown by gas source-molecular beam epitaxy. Aluminum is found to preferentially incorporate into the AlGaN films over the range of fluxes and temperatures investigated [0.05⩽Ji(Ga)⩽0.5 ML/s; 0.1⩽Ji(Al)⩽0.2 ML/s; 700 °C⩽Ts⩽775 °C]. As a result, Ga is not observed to incorporate into the film until the NH3 flux exceeds that required to grow stoichiometric AlN. This preferential incorporation stems from two facts: (a) Al has an ammonia cracking efficiency ∼2.5 times greater than that of Ga, and (b) Al participates in a Al-for-Ga exchange. As a result of these factors and under NH3 limited growth conditions, the aluminum mole fraction in a layer can be controlled by changing the incident NH3 flux.

Heavily carbon-doped InGaP/GaAs HBT's with buried polycrystalline GaAs under the base electrode

This paper describes a new approach to fabricating InGaP/GaAs heterojunction bipolar transistors (HBT's) with a high cutoff frequency (f/sub T/), high maximum oscillation frequency (f/sub max/), and low external collector capacitance (C/sub bc/). To attain a high f/sub T/ and f/sub max/, a heavy carbon-doping (1.3/spl times/10/sup 20/ cm/sup -3/) technique was used with a thin (30-nm-thick) GaAs base layer, while for low C/sub bc/, low-temperature gas-source molecular-beam epitaxial growth on SiO/sub 2/-patterned substrates was used to bury high-resistance polycrystalline GaAs under the base electrode. An f/sub T/ of 120 GHz and an f/sub max/ of 230 GHz were achieved for three parallel 0.7/spl times/8.5 /spl mu/m HBT's with an undoped-collector structure, and an f/sub T/ of 170 GHz and an f/sub max/ of 160 GHz were obtained for a single 0.9/spl times/10 /spl mu/m HBT with a ballistic-collection-transistor structure. Compared to HBT's without buried poly-GaAs, the maximum stable gain was improved by 1.2 dB in the 0.7/spl times/8.5 /spl mu/m HBT and by 2.3 dB in the 0.9/spl times/10 /spl mu/m HBT due to the reduction in C/sub bc/. These results show the high potential of the proposed HBT's for high-speed digital and broadband-amplifier applications.

Study of GSMBE growth and characteristics of high-quality strained [formula omitted] quantum wells

High-quality compressively strained In 0.63 Ga 0.37 As InP quantum wells with different well widths (1–11 nm) have been grown coherently on InP substrates using a home-made gas source molecular beam epitaxy (GSMBE) system. The indium composition in the wells of the sample was determined by means of high-resolution X-ray diffraction and its computer simulation. It is found that the exciton transition energies determined by photoluminescence (PL) at 10 K are in good agreement with those calculated using a deformation potential model. Sharp and intense peaks for each well can be well resolved in the 10 K PL spectra. For wells narrower than 4 nm, the line width of the PL peaks are smaller than the theoretical values of the line-width broadening due to 1 ML interface fluctuation, showing that the interface fluctuation of our sample is within 1 ML. For wells of 7 and 9 nm, the PL peak widths are as low as 4.5 meV.

InGaP/GaAs ballistic collection transistors withburied polycrystallineGaAs under base electrode

InGaP/GaAs ballistic collection transistors, with buried polycrystalline GaAs under the base electrode, have been fabricated by using gas-source molecular beam epitaxial growth on SiO2-patterned GaAs substrates. Heavy C-doping in the base led to a high maximum oscillation frequency of 170 GHz while maintaining a high cutoff frequency of 170 GHz. Owing to the reduction in base-collector capacitance, maximum stable gain was increased by 2.3 dB compared to that of transistors without polycrystalline GaAs.

1.3 µm InAsP/InAlGaAs MQW lasers for high-temperatureoperation

InAsP/InAlGaAs strained multiquantum-well (MQW) 1.3 µm lasers with a large conduction band discontinuity are proposed and demonstrated for the first time. An InAsP/InAlGaAs MQW layer with high structural and optical quality was obtained by gas-source molecular beam epitaxy growth combined with post-growth 650°C rapid thermal annealing. The lasers exhibited a low threshold current density of 1.1 kA/cm2 with an excellent characteristic temperature as high as 116 K.

Thermodynamical properties of thallium-based III-V materials

Thermodynamical factors that affect growth of the thallium-bearing zinc-blende alloys InTIP and InTlAs are examined within the local density approximation (LDA), using the linear muffin-tin orbital method. The LDA predicts TIP and TIAs to be unstable with respect to decomposition into the elemental constituent solids, or marginally stable if conservative estimates of the LDA errors are made. Several thallium-rich and anion-rich compounds have also been examined; some are found to have excess energies per atom comparable to the zinc-blende phase. The equilibrium partial pressures over InTIP and InTlAs have also been calculated as a function of composition. Even with conservative error estimates, we predict that only low concentrations of thallium can be achieved in InTIP (<5% at 350°C) using gas source molecular beam epitaxy (GSMBE), far less than the 67% needed for long-wave infrared (LWIR) applications. Although much less than 1% thallium is predicted to be soluble in InTlAs for GSMBE growth at 350 °C, the addition of error estimates into the calculation indicates that obtaining the 15% thallium needed for LWIR applications may be possible. Native defect populations have been calculated for alloy compositions corresponding to band gaps in the LWIR, and the anion antisite densities are predicted to be quite high, especially in InTIP, reflecting the comparable stability of the TIP and T1P3 phases.

GSMBE growth and characterization of strained-layer MQWs in a P-i-N Configuration

InxGa1-xAs/InP (0.39 less than or equal to x less than or equal to 0.68) strained-layer quantum wells having 20 wells with thickness of 50 Angstrom in a P-i-N configuration were grown by gas source molecular beam epitaxy (GSMBE). High-resolution X-ray diffraction rocking curves show the presence of up to seven orders of sharp and intense satellite reflection, indicative of the structural perfection of the samples. Low-temperature photoluminescence and low-temperature absorption spectra were used to determine the exciton transition energies as a function of strain. Good agreement is achieved between exciton transition energies obtained experimentally at low temperature with those calculated using the deformation potential theory.

Gas-source molecular beam epitaxial growth and characterization of InNxP1−x on InP

We report a study of N incorporation into InP using a radio frequency (rf) N plasma source. Very streaky reflection high-energy electron diffraction patterns are observed for InNxP1−x (x <1%) grown on InP, indicating layer-by-layer growth of the film. The sharp x-ray diffraction peak and the clear Pendelloesung fringes in the high-resolution x-ray rocking curves reveal the high crystalline quality and uniformity of the film. They also suggest the smoothness of the interface between InP and InNxP1−xand of the surface of the InNxP1−x layer. This is further confirmed by scanning electron microscopy on these samples, where featureless surface is obtained. The formation of an InNP alloy is confirmed by x-ray θ-2θ diffraction measurement where no phase separation is observed. Different ways to increase the N composition in InNP were explored. At a fixed N2 flow-rate fraction, lowering the growth temperature increases the N composition in InNP. Raising the rf power or using a larger beam exit aperture will also increase the N incorporation as a result of the availability of more active N species.