LPE Growth Research Articles

InGaP lattice-mismatched LPE growth on GaAs substrates by epitaxial lateral overgrowth technique

The application of the InGaAs/InGaP double-heterostructure laser increases the band offset between the cladding layer and the active layer more than the use of conventional InGaAsP/InP lasers. We propose InGaP lattice-mismatched liquid phase epitaxy on a GaAs substrate by the epitaxial lateral overgrowth (ELO) technique. To obtain the InGaP ( λ=820 nm) cladding layer of the InGaAs ( λ=1.3 μm)/InGaP DH laser, Ga liquid atomic fractions X Ga L were gradually reduced from those of the lattice-matching conditions. The InGaP lattice-mismatched growth on both the GaAs(1 0 0) and (1 1 1)B substrates were successfully carried out by adopting the ELO technique.

MoO 3–Li 2O flux LPE growth of YIG films and its characterization

Pure-Yttrium iron garnet (Y 3Fe 5O 12; YIG) films were grown from a MoO 3–Li 2O flux onto (1 1 1) GGG substrate using liquid phase epitaxy. By investigating the [Fe 2O 3]/[Y 2O 3] molar ratio of the flux, we were able to successfully grow stoichiometric and high-purity YIG films. Evaluations and calculations of lattice mismatch along the 〈1 1 1〉, 〈0 0 1〉, and 〈1 1 0〉 directions using X-ray rocking-curve measurements revealed that these values differed significantly from one another. This clearly indicated that structural deformation had occurred in the YIG films. The deformation was larger in the films grown from the MoO 3–Li 2O flux than in those grown from a PbO–B 2O 3 flux. However, the impurity concentration in the former was one hundred times less than that in the latter. Thus, because of this purity, the YIG films grown from the MoO 3–Li 2O fluxes are preferable for use in optical and microwave devices.

Influence of LPE growth conditions on the electroluminescence properties of InP/InGaAs(P) infrared emitting diodes

Liquid phase epitaxial growth of InP/InGaAs(P) infrared emitting diodes was studied systematically. Small area surface emitting LED chips were prepared to cover completely the 1100–1700 nm wavelength ranges. Nine different diodes were fabricated with optimal spacing of the peak emission wavelengths in order to have sufficient overlapping of their spectra. Efficient LEDs with narrow spectra have been realised by careful selection of the layer structure and growth conditions. Thick active layers with constant composition and abrupt interfaces have been grown for each emission wavelength. The long wavelength diodes (1275–1675 nm) were grown with additional quaternary layer(s) to prevent the melt-back of the active layer by InP melt. Low growth temperature (590°C) was used to prepare the LED structures. In the spectral range of 1250–1520 nm higher growth temperatures (625–645°C) were necessary to improve the device parameters. Such phenomena confirm the existence of the miscibility gap in the InGaAsP quaternary crystal system. Quaternary layers grown in the middle of the immiscibile region showed non-uniform composition and ragged interfaces at the upper heterojunction.

LPE growth of textured single crystal silicon thin film for PV applications

The fabrication of solar cells based on thin silicon film on foreign substrates is an attractive way to realise cheap and efficient photovoltaic devices on a large scale. In this work, we propose an innovative technique to obtain textured monocrystalline Si on mullite owing to the transfer of a nucleation layer and subsequent LPE growth. The nucleation layer (with the shape of a grid) is elaborated by photoelectrochemical etching. The grid pattern parameters will determine the shape of the LPE layer surface, flat or pyramidal textured for efficient light trapping.

Preferential growth mechanism of YBCO film on MgO substrate in initial stage of LPE growth

The mechanism of improving the in-plane alignment of LPE-grown YBCO films on MgO substrate was investigated by the experiments and model analysis. The preferential dissolution and growth of the islands in seed film due to the difference in the in-plane alignment relationship between the island and substrate were observed even when the size of the seed islands were similar. The phenomena can be explained by the coarsening mechanism by considering the difference in the interface energies between YBCO grains and MgO substrate. The preferential growth model was developed based on the above idea. The results of the calculation by the model are in good agreement with the experimental results.

Investigation of rare earth gettering for the fabrication of improved mid-infrared LEDs

The use of a rare earth gettering technique for the growth of very pure InAsSb epitaxial layers of high quantum efficiency and its application for the fabrication of powerful 4.6 /spl mu/m LEDs operating at room temperature is reported. By introducing the rare earth element Gd or Yb into the liquid phase during LPE growth, it is found that the carrier concentration of InAsSb layers can be effectively reduced to /spl sim/6/spl times/10/sup 15/ cm/sup -3/, and that the photoluminescence (PL) intensity of such layers can be considerably increased by between 10 and 100 times compared with untreated material. This behaviour is attributed to the gettering of residual impurities and the corresponding reduction of non-radiative recombination centres in the presence of the rare earth. This technique is used to purify the InAs/sub 0.89/ Sb/sub 0.11/ ternary material in the active region of an InAs/sub 0.55/Sb/sub 0.15/P/sub 0.30/-InAs/sub 0.89/Sb/sub 0.11/ -InAs/sub 0.55/Sb/sub 0.15/P/sub 0.30/ symmetrical double heterostructure LED. A pulsed optical output power in excess of 1 mW at room temperature is measured making these emitters suitable for use in portable instruments for the environmental monitoring of carbon monoxide at 4.6 /spl mu/m.

Sulfide treatment of GaSb surface: influence on the LPE growth of InGaAsSb/AlGaAsSb heterostructures

The influence of Na 2S and (NH 4) 2S treatments on the surface properties of GaSb have been investigated through the etch rate, ellipsometry and Schottky barrier measurements. XRD and TEM analysis were performed to examine the effect of sulfide pretreatment of GaSb substrate on the LPE growth of InGaAsSb/AlGaAsSb heterostructures and their structural quality. Additionally, C–V characteristic of Hg-Schottky barriers were measured to evaluate carrier concentrations in non-intentionally doped InGaAsSb epilayers. Na 2S preepitaxial treatment has been applied to LPE growth of n-In 0.084Ga 0.916As 0.086Sb 0.914/ p-Al 0.45Ga 0.55As 0.02Sb 0.98 LED heterostructures for λ p =2.06 μm and n-In 0.23Ga 0.77As 0.18Sb 0.82/ p-Al 0.24Ga 0.76As 0.02Sb 0.98 PD heterostructures for wavelength λ=2.0–2.4 μm. As a result, LEDs which with increased by a factor of 4 quantum efficiency and total power of 6 mW were obtained. Mesa-structure photodiodes were characterised by detectivity D ∗ λ=2.2 μm =4×10 10 cmHz 1/2 W −1 at room temperature and dark current density j d=16 mA/cm 2 at a reverse bias of −0.5 V.

Impact of CdTe/CdZnTe substrate resistivity on performance degradation of long-wavelength n/sup +/-on-p HgCdTe infrared photodiodes

For realizing HgCdTe focal plane arrays on alternate substrates (Si or GaAs), CdTe buffer layers are essential. Bulk CdTe/CdZnTe substrates are also used for LPE growth of HgCdTe. A model for the effect of the n-CdTe substrate resistivity on the quantum efficiency, /spl eta/, and the dynamic resistance-area product, R/sub d/A, of a n/sup +/-on-p HgCdTe backside illuminated photodiode has been developed, taking into account the effect of the graded heterointerface between CdTe/CdZnTe and HgCdTe on the homojunction photodiode. The issue of how low the substrate/buffer layer resistivity can be, without degrading the performance of the photodiode, has been addressed. For low substrate resistivities, the R/sub d/A can drop by about 50%, while the quantum efficiency decreases by about 5%. It has been found that as low as 2 /spl Omega/-cm for long wavelength IR photodiodes (cutoff wavelength 14 /spl mu/m) is acceptable. To obtain the R/sub d/A and /spl eta/ from the band profile, a linear approximation has been used in which the interface barrier region has a constant electric field, while the bulk of the epilayer has no electric field. General expressions have been derived for the R/sub d/A and /spl eta/ in this two-region model. Our solutions are valid for both high and low electric fields, unlike previously derived solutions in the literature valid either in the one-region low-field case or the two-region, high-field approximation.

TEM investigation of silicon carbide wafers with reduced micropipe density

A technique to reduce the micropipe density in SiC substrates by first filling in the defects and then growing an LPE layer on the filled material has been developed by TDI. LPE growth in SiC is known to result in poor surface morphology, namely step-bunching due to the off-axis substrate orientation. Chemical vapor deposition (CVD) growth experiments on SiC substrates with reduced micropipe density using a cold-wall CVD reactor resulted in a significant improvement in the surface morphology. Although preliminary device results are encouraging, the exact nature of the filled micropipes nor the impact of growing CVD epitaxial layers on LPE SiC had not been fully characterized. We have preformed transmission electron microscopy (TEM) measurements to evaluate the crystallographic properties of the CVD/LPE and LPE/substrate interface. It was observed that no new dislocations were nucleated at the LPE/CVD interface. Although a micropipe was not located in the samples characterized, a tilt of 1.5° was observed between the LPE layer and the substrate. In addition, dislocations were observed to propagate through the LPE layer from the substrate which are most likely the 1C close-core screw dislocations common to SiC hexagonal substrates.

Scaling Analysis of Semiconductor Crystal Growth from the Liquid Phase in an Axis Static Magnetic Field

A formulation of the relation between static magnetic induction and Reynolds number in liquid, for vertical Bridgman and LPE growth processes of semiconductors in axial static magnetic field was derived based on a scaling analysis, and the validity of the estimation was experimentally investigated, The calculated values of the effective segregation coefficients for Ga-doped Ge and Pb 1-x Sn x Te crystals grown by the Bridgman method agreed well with the experimentally measured ones from 0 to 6T of the magnetic induction. In the case of LPE growth on GaP(111)B, nearly diffusion-controlled condition in the liquid was achieved at 6 T. It was shown by in situ observation using a near-infrared (NIR) microscopic interferometer that the static magnetic field reduced the LPE growth rate, and as a result, suppressed appearance of macro-steps and hillocks.

The influence of the high magnetic field to LPE growth process of GaP

The influence of the high magnetic field to LPE growth process of GaP

Study on the LPE growth of InGaAS pyramidal layers on (100) GaAs substrates

Study on the LPE growth of InGaAS pyramidal layers on (100) GaAs substrates

Strain relaxation in PbSnSe and PbSe/PbSnSe layers grown by liquid-phase epitaxy on (1 0 0)-oriented silicon

Ternary PbSnSe layers with various Sn contents were grown by LPE on Si(1 0 0) substrates prepared with MBE-grown PbSe/BaF 2/CaF 2 buffer layers. LPE growth initiation temperatures were varied from 380 to 475°C by changing the chalcogen concentration in the LPE growth solution. PbSe/PbSnSe double layers were also grown using the same procedure. Crack densities and residual strain values in the epilayers were measured by optical Nomarski microscopy and high-resolution X-ray diffraction (HRXRD). Crack densities in Pb 0.91Sn 0.09Se layers decreased from 93 to 33 cracks/cm when the growth temperature was increased from 430 to 475°C. Crystalline quality, as indicated by HRXRD FWHM reduction from 522 to 442 arcsec, also improved with this increase in growth initiation temperature. These results show that IV–VI semiconductor layers grown at higher temperatures are more able to plastically deform when subjected to cooling strain caused by thermal expansion mismatch with the Si substrate. Activation of a strain-relieving higher-order dislocation glide mechanism is a likely explanation for this observation.

Some perspectives and peculiarities of the LPE growth of multicomponent Sb-based solid solutions from pentanary liquid phases

The use of pentanary liquid phases to growth Sb-based solid solutions could improve the quality of these materials and of devices made from them. We discuss here two ways in which these improvements can be achieved. The first one concerns the growth of AlGaAsSb and InGaAsSb from “neutral” solvents in the Sb-rich corner of their phase diagrams. This technology could permit to keep the advantages of growing from Sb solvents and of decreasing the growth temperature at the same time. Another case is related to the control of critical supercooling during LPE growth of AlGaAsSb. We have found experimentally that the addition of In to a Sb-rich Al-Ga-As-Sb liquid phase increases the critical supercooling. In this way the quality of the heterostructure interfaces could be improved.

High quality InAs grown by liquid phase epitaxy using gadolinium gettering

In this paper, we report the growth of very pure InAs epitaxial layers of high quantum efficiency, by introducing the rare-earth element Gd into the liquid phase during LPE growth. We find that the carrier concentration of InAs layers can be effectively reduced to . Also, the peak photoluminescence (PL) intensity of such layers can be considerably increased by between ten- and 100-fold compared with untreated material. We attribute this behaviour to the gettering of residual impurities and corresponding reduction of non-radiative recombination centres in the presence of Gd. Four intense sharp lines dominated the low temperature (4 K) photoluminescense spectra of Gd-treated InAs layers. The strongest two of these were found to originate from (a) bound excitons, and (b) donor-acceptor recombination, whereas the remaining two, (c) and (d), were associated with defect-related recombination. The linewidth (FWHM) of the exciton peak (a) was reduced to only 3.8 meV, which is narrower than for undoped epitaxial InAs grown by MBE or MOVPE.

Electrooptical properties of InP epitaxial layers grown with rare-earth admixture

The influence of rare-earth (RE) elements (Ho, Er and Nd) addition during the LPE growth, on electrooptical properties of InP layers is reported. Temperature dependent Hall effect and capacitance-voltage curves show quite a dramatic impact of Er and Nd on shallow impurity and free-carrier concentrations: they were decreased by as much as three orders of magnitude. The background concentration of both donors and acceptors decrease with increasing of RE content in the melt up to concentrations of about 0.25 wt.%. Low-temperature photoluminescence (PL) spectra have been measured for various levels of excitation power and temperature. The major manifestation of the RE admixture is the pronounced narrowing of PL curves and the corresponding appearence of fine spectral features. Temperature and excitation dependences of shallow acceptor related bands of InP:Nd layers are discussed in more detail.

Effect of built-in electric field on crosstalk in focal plane arrays using HgCdTe epilayers

A simple two-dimensional model, for calculating the effect of the built-in electric field arising in HgCdTe epilayers due to the composition gradient that occurs in LPE growth, on the crosstalk is developed for the case of a back illuminated focal plane array. The calculations predict that the crosstalk does not decrease monotonically with increasing electric field (i.e., weak peaks occur), unlike in the simple one-dimensional model of Kamins and Fong. The zero-field crosstalk varies between 1% and 10%, depending upon the material parameters. For electric fields in the range of 1–10 V cm −1, the crosstalk is reduced to negligible values (<0.01%). The model is approximate to the extent that the effect of the electric field in reducing the crosstalk is somewhat overestimated. The crosstalk depends strongly on the diffusion length and on the absorption coefficient, but very weakly on the diffusion velocity of carriers. The effects of diode size and dead space are similar to those of other models. The effect of the CdTe–HgCdTe interface recombination velocity has been taken into account, whereas that of the top surface recombination velocity has been neglected. The crosstalk to the second nearest neighbour diode is an order of magnitude smaller than that to the first neighbour diode. It goes to zero at a much smaller electric field. The crosstalk is shown to be slightly higher in medium wavelength IR arrays (MWIR) than in long-wavelength IR (LWIR) arrays.

A new LPE growth method of semiconductor heterostructures with thickness profile variation of epitaxial layers

We have investigated and developed a method for the LPE growth of layers with approximately parabolic cross section. The channels were created during the growth process by modulating the liquid phase thickness with W or Mo wires parallel to the substrate. The main parameters of the channel can be controlled by changing the wire’s diameter and its distance from the substrate. This method can be incorporated directly into the growth process of a laser structure with an unstable resonator without the need of additional treatments as chemical etching, to produce the channel structure.

LPE growth of yttrium–lutetium, indium–gallium garnet films for optical waveguide formation on a GGG substrate

Yttrium–lutetium, indium–gallium garnet single-crystal films with a composition of { Y x Lu 3−x}[ Y y1 Lu y2 In y3 Ga 2−y1−y2−y3]( Ga 3) O 12 (0⩽x⩽3, y1=0.02x, y2=0.12−0.04x, y3=1.08−0.11x) were grown on 〈1 1 1〉 - oriented GGG substrate by the LPE technique in order to fabricate a planar optical waveguide. The LPE growth results and optical properties of the films are reported. It was easy to control the composition of the film, because the distribution coefficients of the solutes showed gradual changes with the composition, and the coefficients ratios of Y/Lu and In/Ga, respectively, were 1.33–1.39 and 0.61–1.07. The films had high transparency in the visible and near-infrared regions. In this system, the addition of In increased and refractive index as a result of substitution on the Ga atom site. The films had a refractive index variation of ∼0.7% with the variation in the film composition, and this is large enough for optical waveguide fabrication. To evaluate its optical propagation loss as a waveguide material, a slab waveguide, composed of core and cladding layers, was formed on a GGG substrate. The propagation loss was 1.2 dB/cm at 1523 nm, indicating that the light was confined effectively in the waveguide with a low loss.

The In–As–Sb phase diagram and LPE growth of InAsSb layers on InAs at extremely low temperatures

A calculation of the In–As–Sb phase diagram in the low-temperature range 300–400°C has been made applying the rare simple solution model. By using the calculated data an extremely low temperature LPE was performed for growing InAs 1− x Sb x layers on InAs substrates at temperatures as low as 300°C. It was shown that high-quality layers can be grown on InAs with x up to 0.26. SEM microprobe compositional analysis and X-ray diffraction analysis confirmed their homogeneity and high crystal quality and the promise of this material for mid-infrared optoelectronic devices.