GaAsP Layer Research Articles

Transmission and nanohardness studies of ternary GaAs1-xPx layers grown from the vapor phase by heteroepitaxy

Transmission measurements in the 0.5–25-μm spectral range are performed on thin (<350-μm) GaAsP layers grown by Hydride Vapor Phase Epitaxy (HVPE) on plain (100) GaAs substrates. Comparison with calculations taking into account multiple reflections reveals the role of the surface polishing quality on the clear transmission window and the wavelength dependent losses. A measurement of a 5-mm thick epitaxially grown GaP underlines more realistic spectral limitations on the application of orientation-patterned structures based on GaP and GaAsP for nonlinear optical frequency conversion. The mid-IR cut-off wavelength for the ternary GaAsP layers is almost independent of the composition and corresponds to the same two-phonon absorption limit observed in the binary GaP. Nanohardness and Young's modulus are measured for the same samples to evaluate their compositional dependence. The nanohardness dependence on the P-content obeys a second order polynomial law with a maximum around P = 0.8. Young's modulus depends linearly on the P-content, similar to the trend observed in other ternary systems, such as InxGa1−xAs and InxGa1-xP. The evolution of the band-gap, estimated from the transmission measurements, with the composition of the ternary compounds is linear in the range of 0–0.5 for the P content. In this same range the nanohardness can be considered to be linearly proportional to the band-gap.

The effects of strain compensation in type-II GaAsSb/InGaAs quantum wells grown on GaAs (001) substrates

The effect of the GaAsP strain-compensating layer on type-II GaAs1−xSbx/InyGa1−yAs was investigated. GaAsSb/InGaAs multiple quantum wells (MQWs) without and with GaAsP strain-compensating layers were grown by molecular beam epitaxy. Increasing Sb or In compositions can extend photoluminescence (PL) emission at longer wavelength along with the highly induced compressive strain in the QWs. The power-dependent PL measured at low temperature reveals the type-II band characteristics of the GaAs1−xSbx/InyGa1−yAs system. A detailed analysis of the experimental data reveals that the GaAsP layers compensate the compressive strain of GaAsSb/InGaAs. The type-II QWs with GaAsP layers, (8 nm) GaAs0.84Sb0.16/(2.5 nm) In0.3Ga0.7As/(10 nm) GaAs0.85P0.15, emits PL at ∼1.1 μm, up to 210 K, while the PL of those strained sample without GaAsP vanishes at lower temperature. In view of the described sample, x-ray diffraction (XRD) analysis along with the simulation shows the validity of the procedure, resulting in nearly matched parameters of QW thicknesses and material compositions—(8.9 nm) GaAs0.835Sb0.165/(2.3 nm) In0.3Ga0.7As/(10.3 nm) GaAs0.85P0.15, with those of the designed QW. The thicknesses of QW from the TEM image, (8.6 nm) GaAsSb/(3.1 nm) InGaAs/(10.1 nm) GaAsP, agree well with the XRD results.

Inspection of the Defect State Using the Mobility Spectrum Analysis Method

Mobility spectrum analysis (MSA) is a method that enables the carrier density (and mobility) separation of the majority and minority carriers in multicarrier semiconductors, respectively. In this paper, we use the p-GaAs layer in order to demonstrate that the MSA can perform unique facilities for the defect analysis by using its resolvable features for the carriers. Using two proven methods, we reveal that the defect state can be anticipated at the characteristic temperature in which the ratio () that is associated with the density of the minority carrier , to the density of the majority carrier , exceeds 50%. (1) Using a p-GaAs Schottky diode in a reverse bias regime, the position of the deep level transient spectroscopy (DLTS) peak is shown directly as the defect signal. (2) Furthermore, by examining the current–voltage–temperature (I–V–T) characteristics in the forward bias regime, this peak position has been indirectly revealed as the generation–recombination center. The DLTS signals are dominant around the , according to the window rate, and it has been shown that the peak variation range is consistent with the temperature range of the temperature-dependent generation–recombination peak. The is also consistent with the temperature-dependent thermionic emission peak position. By having only through the MSA, it is possible to intuitively determine the existence and the peak position of the DLTS signal, and the majority carrier’s density enables a more accurate extraction of the deep trap density in the DLTS analysis.

Enhanced Radiative Efficiency of InGaAs/GaAsP Multiple Quantum Wells by Optimizing the Thickness of Interlayers

InGaAs/GaAsP multiple quantum wells (MQWs) are used in electronic devices because the high radiative efficiency of MQWs improves the device performance. To realize high radiative efficiency, a GaAs interlayer is inserted to decrease the defects at the heterointerface between the well and barrier of the MQWs. However, it is unclear how the interlayer thickness and insertion position affect the radiative efficiency of the MQWs. Herein, the influence of the GaAs interlayer thickness on the radiative efficiency by measuring the photoluminescence of MQWs with different interlayer thicknesses is investigated. A thicker GaAs interlayer below the InGaAs enhances the radiative efficiency. Moreover, the GaAs interlayer above the InGaAs must be thicker than ≈6 nm to enhance the radiative efficiency. The initial growth of GaAs above the InGaAs degrades the surface morphology, which may be associated with the carry‐over of indium on the InGaAs surface and may generate defects between the InGaAs and GaAsP layers. The surface of sufficiently thick GaAs interlayers has a flatter morphology and is free from the degradation of radiative efficiency. The results suggest inserting of interlayers with a smooth surface morphology between strained layers during epitaxial growth is an effective method to suppress nonradiative recombination.

Study on the p-type ohmic contact in GaAs-based laser diode

In this paper, the p-GaAs ohmic contact, which is important to improve the conversion efficiency and long-term reliability of high-power optoelectronic devices, was studied. The p-GaAs layer was grown by metal-organic chemical vapor deposition (MOCVD) with a hole concentration of 1.2×1020cm-3, and the metal electrode was fabricated by E-beam evaporation technology based on Ti/Pt/Au metal system. The CTLM tests showed that the p-GaAs contacts were both typical ohmic contact before and after annealing, and the smallest specific contact resistivity of 4.8×10-6Ω·cm2 was obtained after annealing, which mainly due to the direct tunneling effect on the highly doped p-GaAs surface and the formed non-alloy ohmic contact. SEM and EDX analysis showed that the annealing processes used in the n-GaAs metal alloy for laser diode had a little influence on the surface morphology and inter-diffusion of As, Pt, Au elements, while it enhanced the inter-diffusion of Ga and Ti in the contact.

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.

On the Application of Strain-Compensating GaAsP Layers for the Growth of InGaAs/GaAs Quantum-Well Laser Heterostructures Emitting at Wavelengths above 1100 nm on Artificial Ge/Si Substrates

Stressed InGaAs/GaAs quantum-well laser structures are grown by gas-phase epitaxy from organometallic compounds on GaAs substrates and artificial Ge/Si substrates based on Si(001) with an epitaxial metamorphic Ge layer. To suppress the relaxation of elastic stresses during the growth of InGaAs quantum wells with a high fraction of In, strain-compensating GaAsP layers are applied. The structural and radiative properties of the samples grown on substrates of various types are compared. Stimulated radiation at wavelengths up to 1.24 μm at 300 K is obtained for structures grown on GaAs substrates and at wavelengths up to 1.1 μm at 77 K, for structures grown on Ge/Si substrates.

Quantum Well on the n-GaAs Surface Irradiated by Argon Ions

The density of states of the valence band of a p-GaAs layer formed on an n-GaAs surface owing to the bombardment by 2500-eV Ar+ ions has been studied by photoelectron spectroscopy. A number of peaks have been detected in the spectrum of the edge of the valence band in the binding energy range EV < 1.2eV. Their number and energy positions correspond to the quantum confinement levels calculated for a hole quantum well on the surface with the width about the ion penetration depth Rp = 3.6nm. Electronic transitions from these levels to the bottom of the conduction band have been revealed in the spectrum of characteristic energy losses of electrons reflected from the surface. Thus, it has been shown that the action of the argon ion beam on n-GaAs results in the formation of a quantum well on the surface.

Применение компенсирующих слоев GaAsP для роста лазерных гетероструктур с квантовыми ямами InGaAs/GaAs, излучающих на длинах волн больше 1100 нм, на искусственных подложках Ge/Si

AbstractStressed InGaAs/GaAs quantum-well laser structures are grown by gas-phase epitaxy from organometallic compounds on GaAs substrates and artificial Ge/Si substrates based on Si(001) with an epitaxial metamorphic Ge layer. To suppress the relaxation of elastic stresses during the growth of InGaAs quantum wells with a high fraction of In, strain-compensating GaAsP layers are applied. The structural and radiative properties of the samples grown on substrates of various types are compared. Stimulated radiation at wavelengths up to 1.24 μm at 300 K is obtained for structures grown on GaAs substrates and at wavelengths up to 1.1 μm at 77 K, for structures grown on Ge/Si substrates.

Extension of Shockley’s transmission line method (TLM) to characterize ohmic contacts

A method to extract the resistance of the metallic pad of ohmic contacts is presented. It utilizes the transmission line method array of ohmic contacts and measurements required to obtain their specific contact resistance plus just an additional current voltage measure. The method was applied to fully characterize, included their reliability, standard ohmic contacts on p-GaAs and n-GaInP thin epitaxial layers whose measured sheet resistances were 96 and 6.86 (Ohms Sq–1) respectively. Our extended method found contact pad sheet resistances of RshMP = 0.9 and 0.09 (Ohms Sq–1) for those on p-GaAs and n-InGaP, respectively, giving a ratio of 1%–2%, in this case. For their reliability it was found that after 430 °C for a 30 min thermal anneal, those on n-InGaP strongly degrade. The degradation initiates increasing the metallic pad sheet resistance and then the contact resistance, while those on p-GaAs remain unchanged. This method should contribute to a better characterization of ohmic contacts.

Material and Device Improvement of GaAsP Top Solar Cells for GaAsP/SiGe Tandem Solar Cells Grown on Si Substrates

With its wide bandgap and good diode performance, GaAsP is an excellent candidate for the top cell in a silicon-based multijunction tandem device. Even though the material is not lattice matched to silicon, inclusion of a graded SiGe buffer between the GaAsP layer and the Si substrate has previously been demonstrated to enable lattice matching. The SiGe layer may then serve as a high-quality current-matched bottom cell to form a tandem dual-junction structure. This paper describes the design, fabrication, analysis, and improvement of the GaAsP top solar cell in a three-terminal GaAsP/SiGe tandem solar cell on a silicon substrate. Uncertified GaAsP top cell efficiencies have been improved from 8.4% to 18.4% with bandgap voltage offsets ( $W_{{\rm oc}}$ ) of 0.48 and 0.31 V under concentration factors of 1 and 20 ×, respectively. This progress is made by improved III–V material quality, reduced series resistance, and an addition of antireflection coating. Improving the optics, material quality, and fill factor (FF) should further improve the efficiency of the GaAsP top cell in this tandem structure grown on an Si substrate.

Distributed feedback lasers in the 760 to 810 nm range and epitaxial grating design

We present the results from distributed feedback (DFB) lasers with emission wavelengths ranging from 760 to 810 nm and focus on the optimization of Bragg gratings realized with a patterned GaAsP layer that is overgrown with an AlGaAs cladding layer. The impact of the thickness and material composition of the GaAsP grating lines on the DFB laser performance is theoretically and experimentally investigated. 767 nm ridge waveguide DFB lasers with optimized gratings show excellent optoelectronic characteristics in terms of slope efficiency (0.9 W A−1) and linewidth (11 kHz).

Strain effect for different phosphorus content of InGaAs/GaAsP super-lattice in GaAs p–i–n single junction solar cell

The GaAs p–i–n single junction solar cell with InGaAs/GaAsP super-lattice (SL) in the i-region was fabricated by metal organic vapor phase epitaxy (MOVPE). Using the in situ wafer curvature monitoring, a series of SL solar cell samples with different phosphorus composition in the barrier GaAsP layer was evaluated the accumulated strain during MOVPE growth. The sample with larger phosphorus content in GaAsP barrier layer reduced total strain accumulation, resulted in improved solar cell performance regardless to the higher potential barrier. This result indicated the about 3-nm thick barrier is sufficiently thin for carrier extraction by assisting the tunneling effect. Furthermore, the accumulated strain during MOVPE growth of SL deteriorate solar cell.

Unequal P Distribution in Nanowires and the Planar Layer during GaAsP Growth on GaAs {111}B by Metal–Organic Chemical Vapor Deposition

In this study, the behavior of P incorporation GaAsP during ternary nanowires epitaxial growth is investigated. Detailed electron microscopy investigations indicate that (1) the P concentration in the nanowires is higher than that in the simultaneously grown planar layer and (2) the higher growth temperature leads to a higher P concentration in ternary nanowires. We anticipate that the minimization of misfit strain between the GaAsP layer and its underlying GaAs substrate and the complexity of precursor decomposition are responsible for the observed varied P concentrations. These findings implicate that the compositional control in ternary GaAsP nanowires is much more complicated than anticipated.

Effect of compressive strain relaxation on surface morphology in GaAsP growth on GaP substrate

Surface morphology change of GaAs0.6P0.4 and GaAs layer grown on GaP substrate during growth was investigated by an Atomic Force Microscope. The compressive strain in the GaAsP layer was relaxed by {111} plane slips while that in the GaAs layer was relaxed by formation of island structures. During growth, the GaAs layer showed much flatter surface morphology. It was found that the mechanism of the strain relaxation largely affects the surface morphology. Finally, we compared the critical thickness for the {111} plane slip and the transition thickness in which the layer growth mode transits from a layer growth to an island growth to explain the different strain relaxation mechanisms.

Optical characterization of a GaAsSb/GaAs/GaAsP strain-compensated quantum well structure grown by metal-organic vapor phase epitaxy

Optical properties of a strained GaAs0.64Sb0.36/GaAs and a strain-compensated GaAs0.64Sb0.36/GaAs/GaAs0.79P0.21 triple quantum well (TQW) structures were investigated by photoluminescence (PL), photoreflectance (PR) and surface photovoltage spectroscopy (SPS). The samples were grown on GaAs(100) substrates by a horizontal metal-organic vapor phase epitaxy (MOVPE) system. For GaAs0.64Sb0.36/GaAs TQW, a large blueshift of the peak position of PL feature at low temperature with increasing excitation power density and only a very weak PR feature observed in the vicinity of fundamental transitions and were attributed to a weakly type-II heterojunction formed between GaAs0.64Sb0.36 and GaAs. On the other hand, the PR and SPS spectra of GaAs0.64Sb0.36/GaAs/GaAs0.79P0.21 TQW showed a series of intersubband originated transition features, which is a typical characteristic of type-I QW structure. The results revealed that the energy band of QW structures is significantly influenced by the inserted tensile GaAsP layers, which changes the weakly type-II to a type-I structure. The strain-compensated GaAs0.64Sb0.36/GaAs/GaAs0.79P0.21 TQW has a larger overlap integral and hence a higher transition probability, providing a possibility for fabricating high efficiency near infrared laser diodes.

Narrow linewidth 1118/559 nm VECSEL based on strain compensated GaInAs/GaAs quantum-wells for laser cooling of Mg-ions

We report on the development of an optically-pumped vertical external-cavity surface-emitting laser emitting near 1120 nm using strain compensated quantum wells. The development is motivated by the need to achieve narrow linewidth emission at ~280 nm via fourth harmonic generation, which is required to cool Mg+ ions. The gain mirror had a top-emitting geometry, was grown by molecular beam epitaxy and comprised GaInAs/GaAs quantum wells strain compensated by GaAsP layers; the strain compensation was instrumental for achieving a dislocation free epitaxial structure without dark lines. We demonstrate VECSEL operation at a fundamental wavelength close to 1118 nm with a linewidth of less than 300 kHz. Using a lithium triborate crystal we achieved frequency doubling to ~559 nm with an output power of 1.1W.

Characterization of Metamorphic GaAsP/Si Materials and Devices for Photovoltaic Applications

GaAs <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> anion-sublattice compositionally graded buffers and device structures were grown directly on Si(100) substrates by way of a high-quality GaP integration layer, yielding GaAsP target layers having band gaps of photovoltaic interest (1.65-1.8 eV), free of antiphase domains/borders, stacking faults, and microtwins. GaAs <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> growths on both Si and GaP substrates were compared via high-resolution X-ray diffractometry of the metamorphic buffers and deep-level transient spectroscopy (DLTS) of p <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -n diodes that are lattice matched to the final buffer layer. Structural analysis indicates highly efficient epitaxial relaxation throughout the entire growth structure for both types of samples and suggests no significant difference in physical behavior between the two types of samples. DLTS measurements performed on GaAsP diodes fabricated on both Si and GaP substrates reveal the existence of identical sets of traps residing in the n-type GaAsP layers in both types of samples: a single majority carrier (electron) trap, which is located at <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EC</i> - 0.18 eV, and a single minority carrier (hole) trap, which is located at <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">EV</i> + 0.71 eV. Prototype 1.75-eV GaAsP solar cell test devices grown on GaAs <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> P <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-</sub> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">y</i> /Si buffers show good preliminary performance characteristics and offer great promise for future high-efficiency III-V photovoltaics integrated with Si substrates and devices.

Numerical simulation of hydrogenation of GaAs at the cooling stage

Evolution of concentration profiles of all types of hydrogen particles, charge carriers, active doping impurity, and distribution of the electric field in the near-surface layer of hydrogenated p-GaAs during cooling the sample after finishing the stage of introduction of hydrogen is simulated. It is shown that the form of final concentration profiles of hydrogen-containing particles and distribution of the intrinsic electric field in the hydrogenated p-GaAs layer depend on the temperature-time mode of cooling the sample. The degree of the effect of the cooling rate on the final state of hydrogenated layer increases as the doping level of semiconductor is decreased. Systematic features of formation of the final state of the hydrogen-crystal system depending on the cooling rate of the sample are presented and discussed.

Strain of GaAs/GaAsP Superlattices Used as Spin-Polarized Electron Photocathodes, Determined by X-Ray Diffraction

The strains in GaAs/GaAsP superlattices used in spin-polarized photocathodes grown on GaAs and GaP (001) substrates were determined by X-ray diffraction. The thicknesses of the GaAs wells and GaAsP barrier layers were also determined. The band structures of the superlattices were calculated on the basis of these experimentally determined strains and layer thicknesses. The thicknesses and band structures were in good agreement with those observed by transmission electron microscopy and photoluminescence, respectively. The strains induced in the GaAs well layers were approximately linearly dependent upon the phosphorous fraction in the GaAsP layer, and the splitting between the heavy hole band and the light hole band of the superlattices grown on GaP substrates was larger than that of superlattices grown on GaAs substrates. In photocathodes grown on GaP substrates, low polarizations were observed, not due to a lack of band splitting, but to depolarization scattering caused by crystal defects, which were different from that induced in superlattices grown on GaAs substrates. [DOI: 10.1380/ejssnt.2010.125]