Growth Of InGaP Research Articles

Improvement of InGaP solar cells grown with TBP in planetary MOVPE reactor

In this study, the impact of various growth parameters, such as wafer temperature, device structures, and substrate misorientation, on the quality of InGaP epitaxial layers and solar cells grown in a planetary MOVPE reactor using TBP as a P source were investigated and optimized. Results showed that the carrier lifetime in unintentionally n-doped InGaP significantly decreased as the growth temperature increased from 560 to 590 °C. At temperatures above 600 °C, the growth of InGaP was unsuccessful due to extremely rough surface morphology. The study revealed that InGaP rear homojunction and rear heterojunction solar cells using n-type InGaP base layers displayed improved photo-carrier collection and performance compared to traditional front junction solar cells with p-type InGaP base layers. Notably, InGaP grown on GaAs (001) with a 5° miscut towards (111)A was found to have better quality, while InGaP grown on GaAs (001) with a 6° tilt towards (111)B had worse results in terms of carrier lifetime, PL intensity, and solar cell performance.

Growing compound semiconductors

Materials Science Epitaxial growth is the main technique used for depositing nonsilicon integrated electronic and photonic devices. However, methods for growing devices on amorphous and nonepitaxial substrates are limited. Sarkar et al. overcome this by using standing evaporation or sputtering techniques to deposit a metal, such as indium, with a capping oxide layer. The metal is heated in a hydrogen environment, and a precursor is added to convert the metal to the desired target, such as InP, under conditions where only a single nucleation site forms in each patterned site. The versatility of the method is demonstrated through the growth of InP, GaP, InAs, InGaP, SnP, and Sn4P3 crystals directly on SiO2, Si3N4, TiO2, Al2O3, Gd2O3, SrTiO3, and graphene. ACS Nano 10.1021/acsnano.8b01819 (2018).

The influence of atomic ordering on strain relaxation during the growth of metamorphic solar cells

The occurrence of single variant CuPtB ordering during growth of InGaP graded buffer layer structures on offcut (001) GaAs substrates for inverted metamorphic solar cells is found to have a strong influence on strain relaxation mechanisms. Since the surface-induced CuPtB ordering is metastable in the bulk of the material, a strong preference is observed for the nucleation and glide of 60° type misfit dislocations with Burgers vectors that introduce an antiphase boundary into the ordered structure. This results in an overall epitaxial layer tilt in the opposite sense to that normally observed for the direction of substrate offcut. Furthermore, in InGaP buffer layers graded to InP, a switch in the dislocation glide plane preference back to that normally observed for the direction of substrate offcut is observed as the degree of atomic ordering falls below a critical value. This results in the nucleation and glide of new misfit dislocations resulting in an increase in the threading dislocation density that is found to have a deleterious effect on device efficiency. Understanding the materials science behind this behavior will enable the engineering of more effective, lower threading dislocation density strain relief buffer layers resulting in improved performance of subsequently grown devices.

Control of In Surface Segregation and Inter-Diffusion in GaAs on InGaP Grown by Metal–Organic Vapor Phase Epitaxy

In order to fabricate abrupt heterointerfaces of the GaAs/InGaP system by metal–organic vapor phase epitaxy (MOVPE), we studied the In atom distribution by X-ray photoelectron spectroscopy (XPS). The systematic XPS depth profile analyses revealed that the InGaP surface contains an excess amount of In atoms owing to surface segregation. The excess In atoms diffuse into the GaAs layer and cause compositional mixing at the interface of GaAs on InGaP. In order to suppress the interdiffusion and surface segregation of In atoms into GaAs on InGaP, we have developed a novel gas switching sequence for growing GaAs on InGaP. That is, after the growth of InGaP, only tertiarybutylphosphine (TBP) was introduced, and after stopping the supply of TBP, trimethylgallium (TMGa) was pre-introduced to the reactor before the growth of GaAs. Then tertiarybutylarsine (TBAs) was allowed to flow to initiate GaAs growth. This novel gas switching sequence contributed to the formation of abrupt heterointerfaces of GaAs on InGaP.

Growth of Metamorphic InGaP for Wide-Bandgap Photovoltaic Junction by MBE

AbstractMetamorphic triple-junction solar cells can currently attain efficiencies as high as 41.1%. Using additional junctions could lead to efficiencies above 50%, but require the development of a wide bandgap (2.0-2.2eV) material to act as the top layer. In this work we demonstrate wide bandgap InyGa1-yP grown on GaAsxP1-x via solid source molecular beam epitaxy. Unoptimized tensile GaAsxP1-x buffers grown on GaAs exhibit asymmetric strain relaxation, along with formation of faceted trenches 100-300 nm deep in the [01-1] direction. Smaller grading step size and higher substrate temperatures minimizes the facet trench density and results in symmetric strain relaxation. In comparison, compressively-strained graded GaAsxP1-x buffers on GaP show nearly-complete strain relaxation of the top layers and no evidence of trenches. We subsequently grew InyGa1-yP layers on the GaAsxP1-x buffers. Photoluminescence and transmission electron microscopy measurements show no indication of phase separation or CuPt ordering. Taken in combination with the low threading dislocation densities obtained, MBE-grown InyGa1-yP layers are promising candidates for future use as the top junction of a multi-junction solar cell.

Competitive Kinetics Model to Explain Surface Segregation of Indium during InGaP Growth by Using Metal Organic Vapor Phase Epitaxy

An InGaP layer grown by metal organic vapor phase epitaxy (MOVPE) often has an In-rich region within ∼5 nm from the top of the layer. This surface segregation degrades the interface abruptness of InGaP/GaAs systems, which is attractive for high-performance devices such as high electron mobility transistors (HEMTs). This segregation in lattice-matched InGaP/GaAs systems can be explained by considering a “subsurface” in which a surface adsorption layer controls the composition of grown epitaxial layers. In this study, the existence of a subsurface during MOVPE growth of InGaP was experimentally confirmed through kinetic analysis involving a flow modulation method. The kinetic parameters of a subsurface model, such as adsorption and desorption rate constants of each species, were estimated based on experimental data obtained from flow modulation, and then used to successfully explain the In surface segregation in InGaP-MOVPE.

Kinetics of Subsurface Formation during Metal–Organic Vapor Phase Epitaxy Growth of InP and InGaP

InGaP layers grown by metal–organic vapor phase epitaxy (MOVPE) often have an In-rich region within several nanometers from the top of the film, which cannot be explained by normal surface segregation theory. This surface segregation deteriorates the interface abruptness of the InGaP/GaAs system, which is attractive for high-performance devices. This segregation in lattice-matched InGaP/GaAs systems can be explained by considering a “subsurface”, where unstable surface layers play an important role in controlling the composition of grown epi-layers. This subsurface is formed at the beginning of crystal growth, and its thickness is in a steady state under normal continuous epitaxial growth. In this study, the existence of a subsurface during the MOVPE growth of InP and InGaP is experimentally confirmed through kinetic analysis involving a flow modulation method. The kinetic parameters, such as the adsorption and desorption rate constants of In and Ga species, and the crystallization rate from the subsurface are estimated from experimental data and are then used to explain the tendency of In surface segregation in InGaP-MOVPE.

Interlayer formation due to group V-hydride stabilization during interruptions of MOVPE growth of InGaP

The effect of indium and arsenic carry-over and of arsenic–phosphorus exchange on unintentional interlayer formation due to prolonged stabilization under arsine or phosphine during InGaP growth interruptions in metalorganic vapour phase epitaxy (MOVPE) at 580 °C is investigated. Photoluminescence, x-ray diffraction, secondary ion mass spectrometry, transmission electron microscopy and capacitance–voltage (C–V) depth profiling of the electron concentration are used to detect and to characterize possible unintentionally formed interlayers. The C–V measurements show that purging with PH3 mainly enhances the degree of ordering of an interlayer region due to a P-rich reconstruction of the InGaP surface during the growth interruption. The interlayer stress and band offset are too small to be detected by x-ray diffraction or photoluminescence. In contrast, purging with AsH3 during InGaP growth interruption leads to strong arsenic incorporation, but does not lead to any change in the In concentration. The As-rich interlayer gives rise to additional photoluminescence peaks and compressive strain. The relatively large interlayer thickness detected by C–V and SIMS measurements of up to 20 nm indicates that arsenic accumulated during the prolonged growth interruptions carries over into the InGaP layer grown after the interruption. It is shown that the chosen growth conditions suppress the In carry-over, but As carry-over occurs additionally to the As–P exchange.

InP decomposition phosphorus beam source for MBE: design, properties and superlattice growth

The use of GaP and InP crystal decomposition for generating phosphorus molecular beam in MBE growth of multicomponent III-V alloys and multilayer heterostructures involving phosphorus is analysed. The operating characteristics of an InP decomposition phosphorus beam source are presented and MBE growth of InGaP and InGaAsP alloys with controlled composition in both sublattices is described. The usefulness of the source is further demonstrated by growing InGaP/InGaAsP short-period (8 nm) superlattices with high structural perfection as revealed by x-ray diffraction and transmission electron microscopy studies.

Lattice Mismatched LPE Growth of InGaP on Patterned InP Substrate

The performance enhancement of the semiconductor laser for 1.3μm optical communications has been required. But lasing characteristics in the high-temperature operation are poor for the present InGaAsP/InP double-heterostructure (DH) lasers. As a means for solving it, 1.3μm-wavelength InGaAs/InGaP DH lasers with improved temperature characteristics which reduced the leakage current by greatly taking the bandgap difference of cladding layer and active layer is presented. The epitaxial lateral overgrowth (ELO) technique in which growth of the crystal with the large lattice constant difference is possible is very attractive. As a first step of realizing 1.3μm InGaAs/InGaP DH lasers, liquid phase epitaxial growth of the In0.8Ga0.2P (λ=820nm) cladding layer (1.4% lattice mismatched to the InP(100) substrate) was carried out by using the ELO technique.

Lattice Mismatched LPE Growth of InGaP on Patterned InP Substrate

The performance enhancement of the semiconductor laser for 1.3μm optical communications has been required. But lasing characteristics in the high-temperature operation are poor for the present InGaAsP/InP double-heterostructure (DH) lasers. As a means for solving it, 1.3μm-wavelength InGaAs/InGaP DH lasers with improved temperature characteristics which reduced the leakage current by greatly taking the bandgap difference of cladding layer and active layer is presented. The epitaxial lateral overgrowth (ELO) technique in which growth of the crystal with the large lattice constant difference is possible is very attractive. As a first step of realizing 1.3μm InGaAs/InGaP DH lasers, liquid phase epitaxial growth of the In 0.8 Ga 0.2 P (λ=820nm) cladding layer (1.4% lattice mismatched to the InP(100) substrate) was carried out by using the ELO technique.

Control of indium surface segregation in GaAs layer on InGaP grown by MOVPE

ABSTRACTIn order to fabricate good hetero-interface of GaAs/InGaP system by metal-organic vapor phase epitaxy (MOVPE), we studied the indium atom distribution by X-ray photoelectron spectroscopy (XPS). The systematic XPS depth profile analyses of InGaP/GaAs revealed that InGaP surface contains an excess amount of indium atoms. The excess indium atoms diffuse into GaAs layer and cause surface segregation. We have developed a novel gas switching sequence to switch the growth from InGaP to GaAs. That is, after the growth of InGaP, trimethylgallium (TMGa) was pre-introduced to the reactor to terminate the excess amount of indium atoms on InGaP layer. Then tertiarybutylarsine (TBAs) was allowed to flow on the InGaP surface to initiate GaAs growth. This new sequence reduced the amount of indium atoms at the interface and contributed to suppress the inter-diffusion and surface segregation of indium atoms.

Growth and Performance Study of Aluminum-Free InGaAs/GaAs/InGaAsP Strained Quantum-Well Pump Lasers

The growth of InGaP, InGaAs and InGaAsP epilayers lattice matched to GaAs using the low pressure organometallic vapor phase epitaxy (LP-OMVPE) system was investigated. For the application of erbium-doped fiber amplifiers (EDFAs), the emission wavelength and far-field pattern of the pump laser were designed. The optical and electrical performances of the resultant pump laser were measured.

GSMBE growth of InGaP/(In)GaAs modulation-doped heterostructures and their applications to HEMT and HHMT

In this paper we report for the first time gas-source molecular beam epitaxy of both n- and p-channel InGaP/(In)GaAs modulation-doped heterostructure. The sheet density dependence of the two-dimensional hole gas (2DHG) mobility of p-type In 0.49Ga 0.51P/GaAs structures was investigated by Van der Paul Hall measurement at 300 and 77 K. The 2DHG densities of 2.78×10 12 and 1.02×10 12 cm −2 with mobilities of 191 and 2831 cm 2/V s at 300 and 77 K, respectively, for In 0.49Ga 0.51P/GaAs structures have been achieved. Low-temperature and high-magnetic field Hall measurements were also carried out. Longitudinal resistance of the structure shows two oscillations with different periods at a temperature of 0.3 K, indicating that two subbands have been occupied by holes in the GaAs channel. The sheet density for each subband was estimated to be 1.22×10 12 and 0.77×10 12 cm −2, respectively. Both high hole mobility transistors (HHMTs) and high electron mobility transistors (HEMTs) were demonstrated. HHMTs show a maximum DC transconductance of 35 mS/mm. The saturation current is 57 mA/mm at 300 K with V d=−3 V. Both extrinsic transconductance and saturation current of our novel In 0.49Ga 0.51P/GaAs HHMTs are well improved, compared with those of AlGaAs/GaAs and InGaAs/GaAs HHMTs. Enhanced-mode InGaP/InGaAs pseudomorphic HEMTs were achieved with a maximum DC transconductance of 250 mS/mm.

Phosphorus-Species-Induced Band-Gap Anomaly in InGaP Grown by Solid-Source Molecular-Beam Epitaxy

We report on the growth of InGaP by solid-source molecular-beam epitaxy. It is revealed by photoluminescence (PL) that a lower effective band-gap energy appeared when a higher phosphorus cracker temperature was used. Temperature-dependent PL and polarized photoreflectance (PR) also exhibited a weaker atomic ordering effect when the phosphorus cracker temperature increased. Since the variation of the phosphorus cracker temperature significantly changed the P2/P4 ratio, we believe that a more chemically reactive P2 will not only incorporate more In atoms into the epilayer, but will also bring about a smaller composition fluctuation and weaker ordering effect. Therefore, InGaP grown under a more P2-rich condition probably has a higher In content which results in a lower band-gap energy instead of the ordering effect.

Characterization of InGaP/GaAs heterointerfaces grown by metal organic vapour phase epitaxy

In GaAs/InGaP/GaAs structures grown by metal organic vapor-phase epitaxy (MOVPE), the two heterointerfaces are not identical. Normal photoluminescence (PL) features corresponding to the band gaps of GaAs and InGaP are seen for InGaP layer grown on GaAs. However, an intense long-wavelength feature is observed if we grow GaAs on InGaP (inverted structure) while the features of InGaP and GaAs are suppressed. The nature of interfacial regions is investigated by using different gas switching sequences, which can influence the interfacial region composition. Significantly, we find anomalous PL features similar to those observed in the case of inverted structure if we briefly interrupt the growth of InGaP on GaAs and introduce AsH 3 during the growth interruption. Secondary-ion mass spectrometry (SIMS) measurements and preliminary results of the compositional analysis of the interfacial layers based on high resolution X-ray diffraction (HRXRD) and PL measurements suggest that a deleterious effect arises with the exposure of InGaP surface to AsH 3 and is attributed to the formation of an interfacial InGaAsP layer.

Long-wavelength photoluminescence from InGaP/GaAs heterointerfaces grown by metal organic vapour-phase epitaxy

Photoluminescence (PL) and photoluminescence excitation (PLE) spectroscopies are used to investigate the problems related to GaAs/InGaP/GaAs heterointerfaces grown by metal organic vapour-phase epitaxy (MOVPE). Normal PL features corresponding to the band gaps of GaAs and InGaP are seen for InGaP layer grown on GaAs. However, we observe an intense long-wavelength PL feature if we grow GaAs on InGaP while the features of InGaP and GaAs are suppressed. This PL feature varies significantly in wavelength with changes in the switching sequence and it could not be suppressed by the growth of a thin layer of GaP between InGaP and GaAs. Similar PL features are also observed for interrupted growth of InGaP on GaAs if we introduce AsH 3 during the growth interruption. In this case, PLE measurements show that the corresponding PL features arise from an interfacial layer which is created during the interruption and lies sandwiched between the two halves of the InGaP layer. Thus, we show that a deleterious effect arises with the exposure of InGaP surface to AsH 3 during the growth process with or without the Ga source and is attributed to the formation of an interfacial InGaAsP layer.

Solid source molecular beam epitaxial growth of In0.48Ga0.52P on GaAs substrates using a valved phosphorus cracker cell

We report the molecular beam epitaxial growth of InGaP on GaAs (100) substrate using a valved phosphorus cracker cell at various substrate temperatures (T s from 420 °C to 540 °C). Sample characterization was carried out using Raman scattering (RS), photoluminescence (PL) and X-ray diffraction (XRD). Surface morphology characterization was performed using scanning electron microscopy (SEM). Typical InGaP layers showed a lattice mismatch of < 10 -3 and PL full-width at half maximum (FWHM) of ∼ 7 meV at 10 K. The Raman spectrum showed peaks at 330 cm -1 , 360 cm - 1 and 380 cm - corresponding to the transverse-optic (TO), InP-like longitudinal-optic (LO) and GaP-like LO modes, respectively. No Raman signals were detected from the sample grown at substrate temperature (T s ) of 540 °C, due to poor surface morphology arising from indium desorption. A marginal increase in ordering, as evidenced from the slight decrease (∼ 30 meV) in the PL peak energy was seen in samples grown at increasing substrate temperature. Furthermore, no significant variation in the FWHM of the LO modes, TO mode and intensity ratio of the TO mode to the InP-like LO mode were observed, suggesting that any ordering in the material grown using this technique is weak.

Liquid-phase epitaxial growth of InGaP and InGaAsP on GaAs 0.69P 0.31 substrates with application to visible light-emitting diodes

Good-quality In 0.37Ga 0.63P and In 0.2Ga 0.8As 0.27P 0.73 layers lattice-matched to GaAs 0.69P 0.31 epitaxial substrates were grown by liquid-phase epitaxy using a supercooling technique. By selection of an optimum growth condition, we can obtain the undoped layer with a low electron concentration of 3×10 16 cm −3 for In 0.37Ga 0.63P and 2×10 16 cm −3 for In 0.2Ga 0.8As 0.27P 0.73. Photoluminescence (PL) of the undoped, Te- and Zn-doped In 0.37Ga 0.63P and In 0.2Ga 0.8As 0.27P 0.73 layers is described in detail. The emission peaks of 300 and 10 K PL spectra for In 0.37Ga 0.63P and In 0.2Ga 0.8As 0.27P 0.73 are 590 and 568 nm and 639 and 615 nm, respectively. The visible light-emitting diodes (LEDs) employing In 0.37Ga 0.63P/In 0.2Ga 0.8As 0.27P 0.73/In 0.37Ga 0.63P double heterostructure grown on GaAs 0.69P 0.31 substrates were fabricated. The LEDs exhibit a forward-bias turn-on voltage of 1.6–1.7 V, an ideality factor of ∼2.0, an emission wavelength of ∼670 nm and an external quantum efficiency of 0.20% at 60 mA.

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.