Low-pressure Hydride Vapor Phase Research Articles

Heteroepitaxy of GaAsP and GaP on GaAs and Si by low pressure hydride vapor phase epitaxy

Direct heteroepitaxy of GaAsP and GaP on GaAs and on Si by low-pressure hydride vapor phase epitaxy (HVPE) is investigated as prior studies for photovoltaics and non-linear optics applications. When growing GaAsP on GaAs, it is found that the ambient gas during substrate pre-heating influences the ternary composition as well as the crystalline quality of the subsequent growth. GaAs0.72P0.28 with bandgap energy of 1.76 eV has been achieved, which would be suitable for a top cell in Si tandem solar cell structures. Growth of GaP was investigated on planar GaAs as a prior study for realizing orientation patterned (OP) GaP on OP-GaAs. Threading dislocations caused by the 3.6% lattice mismatch between GaP and GaAs are suppressed by adjusting the GaCl flow, achieving a low full width at half maximum of 146 arcsec for the X-ray diffraction omega scan. Direct heteroepitaxy of GaAsP on Si aiming for achieving a GaAsP/Si dual junction solar cell is demonstrated. The inherent problem of initiating nucleation during the direct heteroepitaxy of III-V on Si by HVPE is overcome by utilizing the vapor mixing approach to grow a low-temperature GaP buffer layer on Si, followed by a GaAsP layer grown by conventional HVPE.

Thick hydride vapor phase epitaxial growth of ZnSe on GaAs (1 0 0) vicinal and orientation patterned substrates

Zinc selenide is attractive for numerous optical applications in the mid and longwave infrared from solid state lasers to non-linear optical frequency conversion. Its use has been limited by the availability of single crystal and epitaxial materials. To meet these challenges we have developed a low-pressure hydride vapor phase epitaxy (HVPE) process for growth of high quality thick ZnSe layers on GaAs (1 0 0) vicinal and orientation-patterned GaAs (OP-GaAs) substrates. We show growth of >300 µm thick layers at growth rates >50 µm/hr. With only 0.26% lattice mismatch between ZnSe and GaAs, epitaxial layers with crystal quality comparable to bulk ZnSe substrates are achieved. X-ray reciprocal space maps show the ZnSe to be fully relaxed. Cross-sectional TEM imaging analysis shows stacking faults at the interface that propagate in to the growing film consistent with a full relaxed film. Surface morphology shows the presence of pits that have their long axis perpendicular to [1–10] direction. Low temperature photoluminescence reveals band to band emission that consisted of the 2.797 eV direct band gap along with the strong exciton emission at 2.802 eV. Growth on OP templates revealed low fidelity domains of thickness >50 µm. This work presents a process to produce high quality thick layers potentially suitable for laser and frequency conversion for defense and civilian applications.

Thick orientation-patterned growth of GaP on wafer-fused GaAs templates by hydride vapor phase epitaxy for frequency conversion

Quasi-phase-matched (QPM) GaP layers up to 300 μm thick have been produced by low-pressure hydride vapor phase epitaxy (LP-HVPE) overgrowth on orientation-patterned GaAs (OPGaAs) templates fabricated using a wafer-fusion bonding technique. The growth on the OPGaAs templates resulted in up to 200 μm thick vertically propagating domains, with a total GaP thickness of 300 μm. The successful thick growth on OPGaAs templates is the first step towards solving the material problems associated with unreliable material quality of commercially available GaP wafers and making the whole process of designing QPM frequency conversion devices molecular beam epitaxy free and more cost-effective.

Heteroepitaxial growth of OPGaP on OPGaAs for frequency conversion in the IR and THz

For the first time thick orientation-patterned GaP (OPGaP) was repeatedly grown heteroepitaxially on OPGaAs templates as a quasi-phase matched medium for frequency conversion in the mid and longwave IR, and THz regions. The OP templates were fabricated by wafer-bonding and in a MBE-assisted polarity inversion process. Standard low-pressure hydride vapor phase epitaxy (LP-HVPE) was used for one-step growth of up to 400 µm thick device quality OPGaP with excellent domain fidelity. The presented results can be viewed as the missing link between a well-developed technique for preparation of OP templates, using one robust nonlinear optical material (GaAs), and the subsequent thick epitaxial growth on them of another material (GaP). The reason for these efforts is that the second material has some indisputable advantages in point of view of thermal and optical properties but the preparation of native templates encounters challenges, which makes it difficult to obtain high quality homoepitaxial growth at an affordable price. Successful heteroepitaxial growth at such a relatively high lattice mismatch (- 3.6%) in a close to equilibrium growth process such as HVPE is noteworthy, especially when previously reported attempts, for example, growth of OPZnSe on OPGaAs templates at about 10 times smaller lattice mismatch ( + 0.3%) have produced only limited results. Combining the advantages of the two most promising nonlinear materials, GaAs and GaP, is a solution that will accelerate the development of high power, tunable laser sources for the IR and THz region, which are in great demand on the market.

An InP/Si heterojunction photodiode fabricated by self-aligned corrugated epitaxial lateral overgrowth

An n-InP/p-Si heterojunction photodiode fabricated by corrugated epitaxial lateral overgrowth (CELOG) method is presented. N-InP/p-Si heterojunction has been achieved from a suitable pattern containing circular shaped openings in a triangular lattice on the InP seed layer on p-Si substrate and subsequent CELOG of completely coalesced n-InP. To avoid current path through the seed layer in the final photodiode, semi-insulating InP:Fe was grown with adequate thickness prior to n-InP growth in a low pressure hydride vapor phase epitaxy reactor. The n-InP/p-Si heterointerface was analyzed by scanning electron microscopy and Raman spectroscopy. Room temperature cross-sectional photoluminescence (PL) mapping illustrates the defect reduction effect in InP grown on Si by CELOG method. The InP PL intensity measured above the InP/Si heterojunction is comparable to that of InP grown on a native planar substrate indicating low interface defect density of CELOG InP despite of 8% lattice mismatch with Si. The processed n-InP/p-Si heterojunction photodiodes show diode characteristics from the current-voltage (I-V) measurements with a dark current density of 0.324 mA/cm2 at a reverse voltage of −1 V. Under the illumination of AM1.5 conditions, the InP/Si heterojunction photodiode exhibited photovoltaic effect with an open circuit voltage of 180 mV, a short circuit current density of 1.89 mA/cm2, an external quantum efficiency of 4.3%, and an internal quantum efficiency of 6.4%. This demonstration of epitaxially grown InP/Si heterojunction photodiode will open the door for low cost and high efficiency solar cells and photonic integration of III-Vs on silicon.

High-quality AlN growth on 6H-SiC substrate using three dimensional nucleation by low-pressure hydride vapor phase epitaxy

There is a method of controlling nucleation and lateral growth using the three-dimensional (3D) and two-dimensional (2D) growth modes to reduce the dislocation density. We performed 3D–2D-AlN growth on 6H-SiC substrates to obtain high-quality and crack-free AlN layers by low-pressure hydride vapor phase epitaxy (LP-HVPE). First, we performed 3D-AlN growth directly on a 6H-SiC substrate. With increasing V/III ratio, the AlN island density decreased and the grain size increased. Second, 3D–2D-AlN layers were grown directly on a 6H-SiC substrate. With increasing the V/III ratio of 3D-AlN, the crystalline qualities of the 3D–2D-AlN layer were improved. Third, we performed 3D–2D-AlN growth on a trench-patterned 6H-SiC substrate. The crack density was reduced to relax the stress by voids. We also evaluated the threading dislocation density by using molten KOH/NaOH etching. As a result, the estimated edge dislocation density of the 3D–2D-AlN sample was 3.9 × 108 cm−2.

Towards a monolithically integrated III–V laser on silicon: optimization of multi-quantum well growth on InP on Si

High-quality InGaAsP/InP multi-quantum wells (MQWs) on the isolated areas of indium phosphide on silicon necessary for realizing a monolithically integrated silicon laser is achieved. Indium phosphide layer on silicon, the pre-requisite for the growth of quantum wells is achieved via nano-epitaxial lateral overgrowth (NELOG) technique from a defective seed indium phosphide layer on silicon. This technique makes use of epitaxial lateral overgrowth (ELOG) from closely spaced (1 µm) e-beam lithography-patterned nano-sized openings (∼300 nm) by low-pressure hydride vapor phase epitaxy. A silicon dioxide mask with carefully designed opening patterns and thickness with respect to the opening width is used to block the defects propagating from the indium phosphide seed layer by the so-called necking effect. Growth conditions are optimized to obtain smooth surface morphology even after coalescence of laterally grown indium phosphide from adjacent openings. Surface morphology and optical properties of the NELOG indium phosphide layer are studied using atomic force microscopy, cathodoluminescence and room temperature µ-photoluminescence (µ-PL) measurements. Metal organic vapor phase epitaxial growth of InGaAsP/InP MQWs on the NELOG indium phosphide is conducted. The mask patterns to avoid loading effect that can cause excessive well/barrier thickness and composition change with respect to the targeted values is optimized. Cross-sectional transmission electron microscope studies show that the coalesced NELOG InP on Si is defect-free. PL measurement results indicate the good material quality of the grown MQWs. Microdisk (MD) cavities are fabricated from the MQWs on ELOG layer. PL spectra reveal the existence of resonant modes arising out of these MD cavities. A mode solver using finite difference method indicates the pertinent steps that should be adopted to realize lasing.

AlN Grown on a- and n-Plane Sapphire Substrates by Low-Pressure Hydride Vapor Phase Epitaxy

We have studied the properties of AlN layers grown by low-pressure hydride vapor phase epitaxy (HVPE) on n-plane (112̄3) sapphire substrates and compared them with those of AlN layers on a-plane (112̄0) sapphire substrates. c-Plane AlN was grown on a-plane sapphire. In the case of AlN growth on n-plane sapphire, the c-axis of AlN was tilted by about 1.2° relative to the n-axis of sapphire, unlike AlN growth on a-plane sapphire. For AlN grown on a-plane sapphire, the in-plane epitaxial relationship between AlN and sapphire changed with nitridation temperature in the initial-stage of growth, but it remained constant for AlN grown on n-plane sapphire.

Selective area heteroepitaxy through nanoimprint lithography for large area InP on Si

AbstractThe use of nanoimprint lithography, a low cost and time saving alternative to E‐beam lithography, for growing heteroepitaxial indium phosphide layer on silicon is demonstrated. Two types of patterns on 500 nm and 200 nm thick silicon dioxide mask either on InP substrate or InP seed layer on silicon were generated by UV nanoimprint lithography: (i) circular openings of diameter 150 nm and 200 nm and (ii) line openings of width ranging from 200 nm to 500 nm. Selective area growth and epitaxial lateral overgrowth of InP were conducted on these patterns in a low pressure hydride vapour phase epitaxy reactor. The epitaxial layers obtained were characterized by atomic force microscopy, scanning electron microscopy and micro photoluminescence. The growth from the circular openings on InP substrate and InP (seed) on Si substrate is extremely selective with similar growth morphology. The final shape has an octahedral flat top pyramid type geometry. These can be used as templates for growing InP nanostructures on silicon. The grown InP layers from the line openings on InP substrates are ∼ 2.5 μm thick with root mean square surface roughness as low as 2 nm. Completely coalesced layer of InP over an area of 1.5 mm x 1.5 mm was obtained.The room temperature photoluminescence intensity from InP layers on InP substrate is 55% of that of homoepitaxial InP layer. The decrease in PL intensity with respect to that of the homoepitaxial layer is probably due to defects associated with stacking faults caused by surface roughness of the mask surface. Thus in this study, we have demonstrated that growth of heteroepitaxial InP both homogeneously and selectively on the large area of silicon can be achieved. This opens up the feasibility of growing InP on large area silicon for several photonic applications (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Thick orientation-patterned GaAs grown by low-pressure HVPE on fusion-bonded templates

Quasi-phase-matched GaAs layers up to 600μm thick have been produced by low-pressure hydride vapor phase epitaxy (HVPE) regrowth on templates fabricated using wafer fusion bonding. We have used this combination of techniques to demonstrate an alternative approach for commercial development of orientation-patterned GaAs (OP-GaAs) for nonlinear optical frequency conversion applications. We report on the characterization of this material and present a comparison with OP-GaAs grown using the conventional all-epitaxial templates. The primary advantages of the wafer fusion method are the avoidance of the molecular beam epitaxy growth of GaAs/Ge/GaAs and the ability to use substrates without misorientation. We have observed that some of the misorientation-related growth defects which affect conventional OP-GaAs growth are not as problematic for regrowth on wafer fusion bonded templates. The overall quality of antiphase domain propagation was similar to conventional OP-GaAs layers. A disadvantage was that growth rates were approximately half the values measured for regrowth on misoriented templates.

Epitaxial growth of quasi-phase matched GaP for nonlinear applications: Systematic process improvements

This article presents recent results related to development of thick quasi-phase-matched GaP for incorporation in high power sources radiating in the mid-infrared. The focus was on increasing the growth rate and layer thickness of orientation patterned GaP, while ensuring equal vertical deposition rates and rectangular shape of the domain mesas for both opposite crystallographic lattice orientations. Additionally, we present solutions which confine the presence of uncontrollable hillock growth. The experiments were conducted in a hot-wall horizontal quartz reactor using a standard low-pressure hydride vapor phase epitaxial (HVPE) process. GaP was grown on bare, half-patterned (HP) and orientation-patterned (OP) templates fabricated on (100) GaP and (100) misoriented 4° towards (111)B substrates. The domains were oriented either along the [011] or the [011̄] direction. We compared a sub-lattice inversion MBE assisted process and a wafer fusion bonding technique to create OP templates. When the growth was performed on bare material, the properly chosen growth conditions resulted in reproducible growth of up to 370μm thick layers with high optical, surface and structural quality, grown at a growth rate of 100μm/h in one-hour long experiments and 45μm/h for 8-h long growths. The presence of a core inside the hillocks growing on the layer surface was eliminated. The hillocks were flattened and widened, which allowed often a single hillock to span several domains with alternating opposite crystallographic orientations, when growth was performed on patterned templates. The HP templates were used to determine the optimal substrate and pattern orientations prior to starting growth experiments on OP-templates. As an additional result they revealed that growth could be hillock-free for certain orientations. Growths on OP templates achieved stable growth rates of 50–70μm/h with domain walls propagating vertically. The growth followed the periodicity of the initial pattern. The maximal thickness achieved to date on OP GaP is about 350μm.

In-plane structural anisotropy and polarized Raman-active mode studies of nonpolar AlN grown on 6H -SiC by low-pressure hydride vapor phase epitaxy

Nonpolar a-plane and m-plane AlN layers were grown on a-plane and m-plane 6H-SiC substrates by low-pressure hydride vapor phase epitaxy (LP-HVPE), respectively. The effects of growth temperature were investigated. Results showed that surface roughness was reduced by increasing the temperature for both a-plane and m-plane AlN layers. In-plane morphological anisotropy was revealed by scanning electron microscopy and atomic force microscopy, which was used to image the morphological and structural transitions with temperature. Anisotropy in on-axis X-ray rocking curves was also detected by high-resolution X-ray diffraction. However, compared with the a-plane AlN layer, a smooth surface was easily obtained for the m-plane AlN layer with good crystalline quality. The optimal temperature was lower for the m-plane AlN layer than that for the a-plane AlN layer. The stress characteristics of nonpolar AlN layers were studied using polarized Raman spectra. Results showed the presence of anisotropic in-plane stresses within the epitaxial nonpolar AlN layers.

Influence of off-cut angle of r-plane sapphire on the crystal quality of nonpolar a-plane AlN by LP-HVPE

The effect of the off-cut angle of an r-plane sapphire substrate has been investigated on the growth of a-plane AlN thick layer by low-pressure hydride vapor phase epitaxy (LP-HVPE). The off-cut angle ( θ) was changed from +5.0° (close to c-axis) to −5.0° (close to m-axis). Results show that the crystalline quality and surface morphology are very sensitive to the sign of θ off-angle. The plus θ off-angle is found to be dramatically reduce the full-widths at half-maximum (FWHM) of X-ray rocking curves (XRC), compared with the minus θ off-angle. In-plane FWHM anisotropic feature marked as M- or W-shape dependence on azimuth angle was observed for a-plane AlN. The shape and degree of anisotropy depend on the sign of θ off-angle, while the plus of θ off-angle will leads to the W-shape and the decreased anisotropy. The minimum crystal tilts and twists of the films are observed for the vicinal sapphires with the plus off-angles of +0.2° to +1.0°.

Effects of initial stages on the crystal quality of nonpolar a-plane AlN on r-plane sapphire by low-pressure HVPE

A 4–6 μm thick a-plane (1 1 2¯ 0) AlN was grown on r-plane sapphire substrate by low-pressure hydride vapor phase epitaxy (LP-HVPE), using a direct growth without any nitridation and buffer layer, a single-step nitridation growth, a two-step nitridation growth and a two-step buffer growth method. For the two-step buffer growth procedure, smoother surface is observed with the lower full widths at half maximum (FWHM) of X-ray rocking curves (XRC) compared with the other two kinds of nitridation procedures. A smaller FWHM of in-plane XRC peak anisotropy features are reversed, which is consistent with the smaller in-plane stress anisotropic distribution in a-plane AlN, when the two-step nitridation or buffer growth method is used. In four kinds of initial growth procedures, the two-step buffer method is the suitable method for the growth of a-plane AlN by HVPE with the high crystal quality and more isotropic distribution.

Growth of mm-thick orientation-patterned GaAs for IR and THZ generation

Low-pressure hydride vapor phase epitaxy (HVPE) is being used for the regrowth of thick GaAs on orientation-patterned templates for nonlinear optical frequency conversion. We have achieved epitaxial growth rates of 200 μm/h and produced millimeter-thick films in 10-h-long growth runs. A critical problem in the HVPE regrowth of orientation-patterned GaAs is the preservation of the original patterned structure—during thick growth, the domain walls often bend and annihilate. Measurements indicated that the domain wall bending decreased as the growth temperature was reduced. The substrate miscut and the orientation of unpatterned regions also affect the vertical propagation of domain walls. In this paper we discuss the process improvements which have facilitated the production of millimeter-thick layers with nearly vertical domain walls.

Heteroepitaxy of InP on Silicon-on-Insulator for Optoelectronic Integration

Epitaxial lateral overgrowth of InP was performed on patterned silicon-on-insulator (SOI) and compared with that on Si substrates in a low pressure hydride vapor phase epitaxy system. The InP was characterized by cathodoluminescence. No red shift of peak wavelength was detected for InP/SOI indicating a negligible thermal strain. Additional low energy peaks were found in some regions with a granular structure on the SOI template. A subsequent growth of an InGaAsP/InP MQW (multi quantum well) structure (λ ~ 1.5 µm) was grown on the SOI template and on a planar InP reference sample by metal- organic phase epitaxy. The MQW was characterized by room temperature photoluminescence. A red shift of 35 nm with respect to the reference sample was attributed to the selective-area effect causing thicker wells and/or an increased indium content. Although the PL intensity was weaker than that obtained for the reference, the FWHMs were comparable.

High temperature growth of AlN film by LP‐HVPE

AlN films were grown on AlN/sapphire templates at 1400–1500 °C using low-pressure hydride vapor phase epitaxy (LP-HVPE). Compared to the step-flow growth of AlN film at 1200 °C with growth rate of 2.1 μm/h, AlN films with atomic steps were obtained at 1400–1500 °C even with high growth rate. For the AlN film grown at 1450 °C with growth rate of 14.3 μm/h, the RMS value is 0.75 nm and the FWHM values of (0002) and (10-12) X-ray rocking curve (XRC) are 351 and 781 arcsec, respectively. Since the FWHM value of (10-12) XRC for the AlN/sapphire template is 1492 arcsec, the crystal quality of HVPE-grown AlN is greatly improved compared with the AlN/sapphire template, which is also confirmed by TEM observation. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Fabrication of thick AlN film by low pressure hydride vapor phase epitaxy

AbstractThick AlN crystals were grown by conventional hydride vapor phase epitaxy (HVPE) on AlN/sapphire templates under low pressure (∼15 Torr) at high temperature (1100 °C–1200 °C). Colorless, mirror‐like AlN films were obtained at the growth rates of up to 20.6 μm/h. The best root mean square (RMS) value of atomic force microscope (AFM) observations for the AlN surface was 0.19 nm in a surface of 5×5 μm2. The typical values of full width half maximum (FWHM) of X‐ray rocking curves for (0002) and (10$ \bar 1 $2) diffraction of AlN films were 173–314 arcsec and 1574–1905 arcsec, respectively. We also investigated the influences of carrier gas, growth temperature and growth rate on the crystal quality. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Epitaxial growth of thick GaAs on orientation-patterned wafers for nonlinear optical applications

A method for growing thick epitaxial layers of GaAs on orientation-patterned wafers by low-pressure hydride vapor phase epitaxy is described. For nonlinear optical applications, it is necessary to grow very thick gratings to accommodate the pump laser as it enters through the side and propagates across the patterned layer. The low-pressure method allows for rapid growth at rates well above 100 μm/h on wafers with patterned stripes having 30–500 μm widths. Parasitic deposition of GaAs on the reactor walls upstream of the sample can reduce the growth rate significantly after a few hours. Various techniques are described for eliminating the parasitic growth. Layers over 500 μm thick have been successfully produced during 8 h of growth.

Cathodoluminescence study of orientation patterned GaAs films for non linear optics

ABSTRACTZincblende semiconductor materials such as GaAs and ZnSe are very promising for the generation of tunable IR signals by quasi phase-matched nonlinear optical frequency conversion. Orientation patterned GaAs crystals (OP-GaAs) were grown by low-pressure hydride vapor phase epitaxy (HVPE) on lithographically prepared templates.. Cathodoluminescence (CL) imaging was used to study these epitaxial films, which consist of periodic domains of inverted crystallographic orientation. The challenge is to achieve thick, vertical domains and to minimize sources of optical loss. Both the domain walls and crystal defects may contribute to transmission losses, therefore, a characterization of both is necessary to improve the OP-GaAs crystal performance. The stress and non radiative recombination activity of the domain walls were investigated. The presence of dislocation glide was revealed and CL spectral imaging was used to observe the stress distribution around both the domain walls and the dislocations.