InGaAsP Films Research Articles

Effect of high temperature rapid thermal annealing on optical properties of InGaAsP grown by molecular beam epitaxy

The effect of rapid thermal annealing (RTA) on the optical properties of InGaAsP with band-gap energy of around 1.05 eV for quadruple-junction solar cells grown by molecular beam epitaxy (MBE) has been investigated. The photoluminescence (PL) spectrum of InGaAsP film annealed at 800 °C has strong integrated intensity and low activation energy of band-tail states. The time-resolved PL measurement shows that the decay time of the InGaAsP annealed at 800 °C and as-grown one are 11.6 ns and 3.0 ns at 10 K, respectively. An S-shape PL decay time as a function of temperature for the InGaAsP annealed at 800 °C is observed and is explained by the carrier relaxation dynamics. The RTA process induces reorganization of In and Ga inside the alloy due to the existence of miscibility gap in InGaAsP grown by MBE owing to the Be diffusion at high temperature and results in an increased composition uniformity and an improved PL intensity.

Study on photoluminescence properties of 1.05 eV InGaAsP layers grown by molecular beam epitaxy

The photoluminescence properties of InGaAsP films with a bandgap energy of 1.05 eV for quadruple-junction solar cells grown by molecular beam epitaxy (MBE) are investigated. We make the excitation intensity and temperature dependence of continuous-wave photoluminescence (cw-PL) measurements. The PL peak position is 1.1 eV at 10 K, and almost independent of the excitation power, but the integrated intensity of the PL emission peaks is roughly proportional to the excitation power. The shift of peak position with temperature follows the band gap shrinking predicted by the well-known Varshni's empirical formula. These results indicate that the intrinsic transition dominates the light emission of the InGaAsP material. In addition, we also make the time-resolved photoluminescence (TRPL) measurements to determine the carrier luminescence relaxation time in InGaAsP. PL spectra suggest that the relaxation time is 10.4 ns at room temperature and increases with increasing excitation power, which demonstrates the high quality of the InGaAsP material. However, the relaxation time shows an S-shape variation with increasing temperature: it increases at temperatures lower than 50 K, and then decreases between 50–150 K, and increases again when temperature is over 150 K. According to the effect of temperature and the non-radiative recombination center concentration on the carrier relaxation time, the recombination mechanism of S-shape variation can be explained by the carrier relaxation dynamics.

InGaAsP/InGaP superlattices by conventional MBE with molten metal solution phosphorus source

A phosphorus beam source utilizing thermal decomposition of InP is employed in a molecular beam epitaxy system. Quaternary InGaAsP films with reproducible P and As contents in the group V sublattice, and high-quality InGaAsP/InGaP superlattices with 10 and more periods were grown on (0 0 1) GaAs substrates.

Epitaxial growth, electronic properties, and photocathode applications of strained pseudomorphic InGaAsP/GaAs layers

The results of experimental and theoretical investigations directed toward the development of highly efficient sources of spin-polarized electrons are reported. The sources are based on heteroepitaxial elastically strained films of the quaternary InGaAsP solid solution grown by liquid-phase epitaxy on GaAs substrates. The InGaAsP films synthesized were 0.1–0.2 µm thick with the band gap being within the range of 1.4–1.9 eV and having elastic strains as high as 1%. This provided splitting of the valence band top by 40–60 meV and a degree of the spin polarization P of the electrons photoemitted as high as 80%. The films have a high quantum yield of photoemission Y upon activating to the negative electron affinity state due to the adsorption of Cs and O. Record values for the effective figure of merit P2Y are achieved.

Physical properties of InGaAsP/InP grown by molecular beam epitaxy with valve phosphorous cracker cell

InGaAsP films grown on InP substrate by solid source molecular beam epitaxy (SSMBE) using a valve phosphorous cracker cell are investigated. It is found that the films grown at flux ratios f As/( f As+ f p) from 0.45 to 0.50 show a superior quality. It is also found that As pressure plays a crucial role in the scattering process; for the films grown at higher arsenic beam pressure (BEP), the Hall mobility μ is dominated by impurity scattering, polar phonon scattering and alloy scattering. For the films with high quality, optical scattering and alloy scattering dominate the mobility. The exponent of T for the films grown at low BEP is found to be as high as 2.54, which cannot be explained by impurity scattering alone. It is believed that, in addition to the impurity-related scattering, some defects associated with As vacancies also significantly contribute to the scattering, especially at low temperatures.

Characterization of heavily carbon-doped InGaAsP layers grown by chemical beam epitaxy using tetrabromide

Carbon doping in InGaAsP films using tetrabromide (CBr4) in chemical beam epitaxy has been studied, focusing on the relationship between the composition and the carrier concentration. The films with an equivalent wavelength of more than 1.4 μm have p-type conduction while the films with less than 1.3 μm have n-type conduction. Specifically, the hole concentration decreases from 7×1019 to 7×1018 cm−3 with decreasing wavelength in the 1.4–1.66 μm range, while electron concentration increases from 5×1018 to 2×1019 cm−3 with decreasing wavelength in the 1.1–1.3 μm range. Secondary-ion mass spectroscopy reveals that the incorporated carbon atom concentration is the same between an InGaAs film and a 1.4 μm equivalent wavelength InGaAsP film under a fixed CBr4 flux. Increase in gallium mole fraction monotonously increases hole concentrations under a fixed group-V mole fraction. We have found that the In1−xGaxAs1−yPy conduction type is mainly determined by two parameters: the Ga and P mole fractions, i.e., p type if x>y.

Compositional variations in InGaAsP films grown on patterned substrates

A comparison of the growth behaviour of lattice-matched In 0.53 Ga 0.47 As and In 0.74 Ga 0.26 As 0.59P 0.41 films on InP substrates, patterned as diffraction gratings, has been carried out using analytical electron microscopy. Ga enrichment above the ridge of the grating was found in both the ternary and quaternary alloys. In the final stages of growth of a 100 nm thick ternary alloy film, the Ga enrichment was confined to a narrow strip, 3 nm in width, lying directly above the ridge. The partitioning of alloying elements during growth led to regions of the film that were locally under tension or compression, as seen by diffraction contrast. The films showed strikingly different planarization behaviour that appears to correlate with the In content.

In situ reflectance monitoring of InP/InGaAsP films grown by metalorganic vapor phase epitaxy

We report the use of in situ reflectance spectroscopy for real-time monitoring of the metalorganic vapor phase epitaxy (MOVPE) growth of InGaAsP films. In situ optical measurements have not been previously reported for this materials system because of its strong absorption in the spectral range of commonly available detectors (λ<1100 nm). To acquire reflectance data beyond the absorption regions of these films we used a grating spectrometer with a Si/PbS dual detector having a wavelength range of 400–2500 nm. Measurements were made during growth of InP/InGaAs/InP double heterostructures and 1.3 μm InGaAsP MQW laser device structures. The multiwavelength reflectance data enabled extraction of the film optical constants, determination of deposition rates to better than 1%, and provided nanometer scale thickness sensitivity for MQW samples.

Highly strained InGaAsP films with high critical thicknesses

Elastically strained InGaAsP films with band gaps from 1.4 to 1.8 eV were grown on GaAs(111)B substrates by liquid phase epitaxy. For elastic strains up to 1% the critical thicknesses of the films substantially exceeded the predictions of the energy equilibrium theory by Matthews and Blakeslee. Among the various stress-relieving mechanisms proposed in the literature a stress-induced surface roughening has been found to be most relevant in our case.

Effect of temperature on InGaAsP alloy composition

The influence of growth temperature on the composition of InGaAsP films grown by low pressure metalorganic vapor phase epitaxy (MOVPE) is reported for quaternary (Q) alloys having bandgap wavelengths of λg = 1.1, 1.3, and 1.5 μn. Films with these different Q-compositions were deposited lattice matched to InP at a growth temperature of 675°C. Subsequent growth experiments were then performed for each Q-composition in which the input gas flow rates were kept the same and only the temperature changed in 25°C decrements down to 600°C. Photoluminescence (PL) and lattice mismatch (LMM) measurements of the resulting films were used to determine the effect of growth temperature on film composition. The PL data indicate a temperature shift in the PL wavelength of −1.8 nm/ °C for the 1.5Q composition, −2.9 nm/°C for 1.3Q, and −4.3 nm/°C for 1.1Q. Negative shifts were also observed in LMM of −80 ppm/°C for 1.5Q, −150 ppm/°C for 1.3Q, and −250 ppm/°C for 1.1Q. The Ga/In and P/As ratios of the Q-filmswere measured by secondary ion mass spectroscopy and correlated with full-wafer maps of the PL wavelength and lattice mismatch to gain insight into the processes responsible for wafer nonuniformity in MOVPE.

Elastically strained InGaAsP films grown by LPE and conception of stress-induced supercooling

The pseudomorphic InGaAsP films with elastic strains up to 1% are grown on GaAs substrates of (111)B orientation by liquid phase epitaxy (LPE). The evolution of morphology with an increase of elastic strain in the films is analysed. A new mechanism of elastic strain relaxation during InGaAsP film growth is discovered. It consists in the appearance of unstrained islands in the InGaAsP strained film and their lateral spreading till they come together. The fundamental limit of elastic strains to about 1% in the InGaAsP films grown by LPE is connected with the stress-induced supercooling that appears and increases with the stresses in the film and, at last, compensates the initial supercooling of the liquid. The time required for the growth of the elastically strained films does not exceed a few seconds. At longer duration of the growth unstrained parts of the film spread laterally and cover the whole surface of the substrate with a highly mismatched unstrained layer of poor crystal quality. [Russian Text Ignored].

Characterization of Magneto-Optical Rare Earth-Doped Ingaasp Thin Films on InP

AbstractWe have investigated the properties of rare earth-doped InGaAsP thin films with special interest in magneto-optical device applications. Magneto-optical properties have been used in optical systems as isolators, waveguides, and switches. These materials and devices can be used to expand the functionality of InP opto-electronic integrated circuits (OEICs). Thin films of InP, InGaAs, and InGaAsP, grown by liquid phase epitaxy, were lattice matched to the (100) InP substrates. The films were n-type, with the carrier concentration decreasing by an order of magnitude in the doped films due to gettering by the rare earth elements. The doped films contained 2.6×1018 - 1.5×1020 cm−3 rare earth elements, which were observed to segregate toward the film/melt interface in the more highly doped films. A broad photoluminescence was observed at 1.52 μm in the Er-doped films. The Verdet constant was measured through the sample thickness, and the substrate signal dominated the measurements. However, the measured values were in agreement with published values for InP, which gives an indication of the films' host value. The Verdet constants increased from 4 to 7 deg/T/mm as the wavelength decreased toward the band edge. The band edges of our samples were 0.93, 1.62, and 1.30 μm, respectively. Rare earth dopants were observed to raise the refractive index of the InP films, and waveguiding at 1.3 μm was achieved in the rare earth-doped InP films and in the InGaAsP films.

Liquid phase epitaxial growth of elastically strained InGaAsP layers for spin-polarized electron sources

InGaAsPGaAs(111)B pseudomorphic layers have been grown with elastic strains up to 1% and bandgaps ranging from 1.4 to 1.8 eV by liquid phase epitaxy (LPE) for the first time. Splitting of the valence band up to 50 meV was observed in these films. Photoemitters with the negative electron affinity state have been prepared by CsO activation of the strained InGaAsP films in ultrahigh vacuum (UHV).

Passive Q switching of Nd:YAG lasers by use of bulk semiconductors

We report passive Q switching of Nd:YAG lasers with the use of a bulk InGaAsP film, grown on an InP substrate by liquid-phase epitaxy, as an intracavity saturable absorber. The single Q-switched pulse had a maximum energy of 1.65 mJ with a 20-ns duration. The simple technology is easily extendible to any infrared solid-state laser.

Chemical beam epitaxy of InP, InGaAs and InGaAsP on non-planar InP substrates

The authors report the growth behavior of the InP, InGaAs and InGaAsP on non-planar InP substrates where ridges were formed with (111)A, (211)A, (111)B and (551) sidewall planes. All three materials grow uniformly on the whole patterned surface with (111)A and (211)A sidewall planes. They grow separately on the plateau and in the valley for the other two structures. The growth front of the InGaAs films is always rippled near the sidewalls, indicating large deviations from lattice-matched composition in these areas, while the growth front in the case of the InP and InGaAsP films remains smooth. Single-step growth of buried double heterostructures with a 1 mu m wide rib is realized for the structures with both (111)B and (551) sidewall planes. The growth mechanisms responsible for the observed features are discussed.

Gas-source molecular-beam epitaxial growth of InGaAsP for 1.3 μm distributed Bragg reflectors

High-quality InGaAsP films were grown on (100) InP substrates by gas-source molecular-beam epitaxy for use in distributed Bragg reflectors (DBR) operating at the wavelengths of 1.1–1.4 μm. By adjusting the inlet pressures of the feedstock gases AsH3 and PH3, precise control of the InGaAsP film composition was reproductively obtained, as evidenced by lattice mismatch of ≤ 5 × 10−4 and band-gap wavelength variation of ≤10 nm. The InGaAsP films exhibited x-ray diffraction peak widths as small as 21 arcsec and a low-temperature photoluminescence peak width of 4.6 meV. Using 35.5 periods of alternating quarter wavelength layers of InGaAsP (1.15 μm composition) and InP, a DBR with a maximum reflectivity of 96±2% at the wavelength of 1.31 μm is demonstrated.

Determination of the composition of strained InGaAsP layers on InP substrates using photoreflectance and double-crystal x-ray diffractometry

Determining the composition of strained InGaAsP films through measurements of the lattice spacings and band-gap energies (Eg) requires converting the measured values to ones which would correspond to unstrained material. In strained layers the lattice constants perpendicular and parallel to the growth plane can vary significantly from the relaxed value, and the optically measured Eg is affected by a strain-induced splitting of the valence band and a shifting of the direct gap energy. By combining double-crystal x-ray data with room-temperature photoreflectance results, we determine the InGaAsP composition accurately using an iterative procedure. Film compositions calculated using strain adjusted values of Eg agree with those determined by energy dispersive spectroscopy to within 1–2 at. %, whereas if energy shifts are not considered, the error approaches 10 at. % for strain on the order of 0.4%.

Growth of InGaAsP films in a Multi-Wafer high Speed Rotating Disk Reactor by Mocvd

AbstractAs the demands for InP epitaxial materials grow, the need for larger throughput growth techniques becomes important. However, uniformity of thickness and particularly composition of InGaAs and InGaAsP films has proved troublesome. This has limited much of the InGaAsP growth work to single wafer machines. The purpose of this work is to demonstrate good film properties and uniformity on a multi-wafer machine that holds three, two-inch diameter wafers.

Application of x-ray topographic methods to thin film electronic materials

X‐ray methods are presented which, besides offering a topographic survey of the defect structure in electronic materials, give quantitative information on the induced strain distribution. Complete strain tensor analyses are obtained by the back‐reflection divergent beam method and by the method of computer‐aided rocking curve analysis (CARCA). The latter is based on the double‐crystal diffractometer principle. An example of the strain analysis by CARCA is given showing the strain dependence on the thickness variation of an InGaAsP film grown on a substrate of InP. Valuable information on the density of interface dislocation is obtained by combining these methods with lattice curvature measurements using scanning topography with automatic Bragg angle control. The elucidation of the strain distribution in depth becomes enhanced by application of x radiation of various wavelengths.

Acoustic phonon generation in the picosecond dynamics of dense electron-hole plasmas in InGaAsP films

Oscillations superposed on transient transmission and reflection from submicron films of InGaAsP (Eg=0.96 eV) and GaAs excited by subpicosecond optical pulses have been observed. The oscillations are due to coherent acoustic phonon generation in the thin films. Values for the velocity of sound, and the band-gap variation due to hydrostatic pressure and the difference in acoustic deformation potentials between conduction and valence bands are determined by analyzing the period and magnitude of the oscillations.