Etch Pit Density Research Articles

Heteroepitaxial Growth of Germanium-on-Silicon Using Ultrahigh-Vacuum Chemical Vapor Deposition with RF Plasma Enhancement

Germanium (Ge) films have been grown on silicon (Si) substrate by ultrahigh-vacuum chemical vapor deposition with plasma enhancement (PE). Argon plasma was generated using high-power radiofrequency (50 W) to assist in germane decomposition at low temperature. The growth temperature was varied in the low range of 250°C to 450°C to make this growth process compatible with complementary metal–oxide–semiconductor technology. The material and optical properties of the grown Ge films were investigated. The material quality was determined by Raman and x-ray diffraction techniques, revealing growth of crystalline films in the temperature range of 350°C to 450°C. Photoluminescence spectra revealed improved optical quality at growth temperatures of 400°C and 450°C. Furthermore, material quality study using transmission electron microscopy revealed existence of defects in the Ge layer grown at 400°C. Based on the etch pit density, the average threading dislocation density in the Ge layer obtained at this growth temperature was measured to be 4.5 × 108 cm−2. This result was achieved without any material improvement steps such as use of graded buffer or thermal annealing. Comparison between PE and non-plasma-enhanced growth, in the same machine at otherwise the same growth conditions, indicated increased growth rate and improved material and optical qualities for PE growth.

Effect of Sn Composition in Ge1−xSn x Layers Grown by Using Rapid Thermal Chemical Vapor Deposition

The Ge1−xSn x layers were grown by using rapid thermal chemical-vapor deposition (RTCVD) on boron-doped p-type Si (100) substrates with Sn compositions up to x = 0.83%. In order to obtain effect of the Sn composition on the structural and the optical characteristics, we utilized highresolution X-ray diffraction (HR-XRD), etch pit density (EPD), atomic force microscopy (AFM), Raman spectroscopy, and photocurrent (PC) spectra. The Sn compositions in the Ge1−xSn x layers were found to be of x = 0.00%, 0.51%, 0.65%, and 0.83%. The root-mean-square (RMS) of the surface roughness of the Ge1−xSn x layer increased from 2.02 nm to 3.40 nm as the Sn composition was increased from 0.51% to 0.83%, and EPD was on the order of ~ 108 cm−2. The Raman spectra consist of only one strong peak near 300 cm−1, which is assigned to the Ge-Ge LO peaks and the Raman peaks shift to the wave number with increasing Sn composition. Photocurrent spectra show near energy band gap peaks and their peak energies decrease with increasing Sn composition due to band-gap bowing in the Ge1−xSn x layer. An increase in the band gap bowing parameter was observed with increasing Sn composition.

MBE-growth of CdTe on GaSb substrates: A case study on the influence of substrate quality

CdTe epitaxial layers were grown by MBE on GaSb (211)B substrates from two different suppliers in order to determine the influence of as-received substrate quality on the material quality of subsequently-grown CdTe epilayers. It is observed that GaSb substrates with smooth surface and lower degree of surface roughness can lead to CdTe epilayers with superior material quality, as evidenced by a lower dislocation density, lower etch pit density, lower degree of epilayer surface roughness, narrower XRD FWHM, and lower strain. It is concluded that in comparison to substrates with a relatively smooth surface (RMS surface roughness ∼ 0.62 nm), substrates with a high degree of surface roughness (RMS surface roughness ∼ 2.24 nm) lead to effects that generate misfit dislocations during the MBE growth process. This results in approximately an order of magnitude increase in measured etch pit density (from ∼9 × 105 to 7 × 106 cm−2) and the calculated dislocation density (from 6.51 × 105 to 6.87 × 106 cm−2, as determined from X-ray diffraction reciprocal space mapping), indicating that a smooth substrate surface is critical in achieving high quality CdTe epilayers on GaSb.

Crystal growth, structural, optical, thermal, mechanical, laser damage threshold and electrical properties of triphenylphosphine oxide 4-nitrophenol (TP4N) single crystals for nonlinear optical applications

The optically good quality single crystals of triphenylphosphine oxide 4-nitrophenol (TP4N) with maximum dimension of 15 × 10 × 5 mm3 were grown by slow evaporation solution technique (SEST) at room temperature. The cell dimensions of the grown TP4N crystal were confirmed by single crystal X-ray diffraction (SXRD) and the crystalline purity was confirmed and planes were indexed by powder X-ray diffraction (PXRD) analysis. Functional groups of TP4N crystal were confirmed by Fourier transform infrared (FTIR) spectral analysis. The optical transmittance of the grown crystal was determined by the UV–Vis NIR spectral analysis and it has good optical transparency in the entire visible region. The band tail (Urbach) energy of the grown crystal was analyzed and it appears to be minimum, which indicates that the TP4N has good crystallinity. The position of valence band (Ev) and conduction band (Ec) of the TP4N have been determined from the electron affinity energy (EA) and the ionization energy (EI) of its elements and using the optical band gap. The thermal behaviour of the grown crystal was investigated by thermogravimetric and differential thermal analysis (TG-DTA). Vickers microhardness analysis was carried out to identify the mechanical stability of the grown crystal and their indentation size effect (ISE) was explained by the Meyer’s law (ML), Hays-Kendall’s (HK) approach, proportional specimen resistance (PSR) model, modified PSR model (MPSR), elastic/plastic deformation (EPD) model and indentation induced cracking (IIC) model. Chemical etching study was carried out to find the etch pit density (EPD) of the grown crystal. Laser damage threshold (LDT) value was measured by using Nd:YAG laser (1064 nm). The dielectric permittivity (ε՛) and dielectric loss (tan δ) as a function of frequency was measured. The electronic polarizability (α) of the TP4N crystal was calculated. It is well matched to the value which was calculated from Clausius-Mossotti relation, Lorentz-Lorentz equation, optical band gap and coupled dipole method (CDM). The Z-scan technique was carried out using solid state laser (640 nm) to analyze the nonlinear optical properties of the TP4N crystal. It exhibits the self-defocusing and saturable absorbance effect during analysis of closed and open aperture respectively. The nonlinear optical parameters such as refractive index (n2), absorption coefficient (β) and the third order nonlinear optical susceptibility (χ(3)) were analyzed.

Spectroscopic and microscopic investigation of MBE-grown CdTe (211)B epitaxial thin films on GaAs (211)B substrates

CdTe epitaxial thin films, for use as a buffer layer for HgCdTe defectors, were grown on GaAs (211)B using the molecular beam epitaxy method. Wet chemical etching (Everson method) was applied to the epitaxial films using various concentrations and application times to quantify the crystal quality and dislocation density. Surface characterization of the epitaxial films was achieved using Atomic force microscopy and Scanning electron microscopy (SEM) before and after each treatment. The Energy Dispersive X-Ray apparatus of SEM was used to characterize the chemical composition. Untreated CdTe films show smooth surface characteristics with root mean square (RMS) roughnesses of 1.18–3.89 nm. The thicknesses of the CdTe layers formed were calculated via FTIR spectrometry and obtained by ex situ spectroscopic ellipsometry. Raman spectra were obtained for various temperatures. Etch pit densities (EPD) were measured, from which it could be seen that EPD changes between 1.7 × 108 and 9.2 × 108 cm−2 depending on the concentration of the Everson etch solution and treatment time. Structure, shape and depth of pits resulting from each etch pit implementation were also evaluated. Pit widths varying between 0.15 and 0.71 µm with heights varying between 2 and 80 nm were observed. RMS roughness was found to vary by anything from 1.56 to 26 nm.

Influences of ultrathin amorphous buffer layers on GaAs/Si grown by metal–organic chemical vapor deposition

In this work, a technique for the growth of GaAs epilayers on Si, combining an ultrathin amorphous Si buffer layer and a three-step growth method, has been developed to achieve high crystalline quality for monolithic integration. The influences of the combined technique for the crystalline quality of GaAs on Si are researched in this article. The crystalline quality of GaAs epilayer on Si with the combined technique is investigated by scanning electron microscopy, double crystal X-ray diffraction (DCXRD), photoluminescence, and transmission electron microscopy measurements. By means of this technique, a 1.8-µm-thick high-quality GaAs/Si epilayer was grown by metal–organic chemical vapor deposition. The full-width at half-maximum of the DCXRD rocking curve in the (400) reflection obtained from the GaAs/Si epilayers is about 163 arcsec. Compared with only using three-step growth method, the current technique reduces etch pit density from 3 × 106 cm−2 to 1.5 × 105 cm−2. The results demonstrate that the combined technique is an effective approach for reducing dislocation density in GaAs epilayers on Si.

Novel report on SHG efficiency, Z-scan, laser damage threshold, photoluminescence, dielectric and surface microscopic studies of hybrid inorganic ammonium zinc sulphate hydrate single crystal

Hybrid inorganic nonlinear optical crystals find huge applications in laser assisted photonic devices therefore present communication firstly aims to investigate the dielectric, microscopic and linear-nonlinear optical properties of ammonium zinc sulphate hydrate (AZSH) crystal. The inorganic AZSH complex has been synthesized and 15 × 10 × 09 mm3 single crystal was grown by slow solvent evaporation method. The powder and single crystal X-ray diffraction technique has been employed to evaluate the crystalline phase and determine the structural parameters of AZSH crystal. The optical transparency of AZSH crystal has been examined within the wavelength rage of 200–1100 nm. The enhanced second harmonic generation efficiency of AZSH crystal is 2.53 times higher than standard KDP crystal. The laser damage threshold of AZSH crystal has been determined using the Nd:YAG laser operating at 1064 nm. The close and open aperture Z-scan studies have been performed to ascertain the nature of third order nonlinear optical (TONLO) refraction and absorption of AZSH crystal. The order of TONLO parameters n2, β and χ3 is found to be 10−9 cm2/W, 10−4 cm/W, 10−4 esu respectively. The AZSH crystal is found to have violet colored luminescence emission centered at 370 nm. The dielectric constant and dielectric loss of AZSH crystal has been evaluated within 30 Hz to 1 MHz. The chemical etching technique has been imposed to examine the growth habitat and determine the etch pit density of AZSH crystal.

Lateral overgrowth of diamond film on stripes patterned Ir/HPHT-diamond substrate

Epitaxial lateral overgrowth (ELO) of diamond films on patterned Ir/(0 0 1)HPHT-diamond substrates have been carried out by microwave plasma CVD system. Ir/(0 0 1)HPHT-diamond substrates are fabricated by photolithographic and magnetron sputtering technique. The morphology of the as grown ELO diamond film is characterized by optical microscopy and scanning electronic microscopy. The quality and stress of the ELO diamond film are investigated by surface etching pit density and micro-Raman spectroscopy. Two ultraviolet photodetectors are fabricated on ELO diamond area and non-ELO diamond area prepared on same substrate, and that one on ELO diamond area indicates better photoelectric properties. All results indicate quality of ELO diamond film is improved.

MOVPE growth of nitrogen- and aluminum-polar AlN on 4H-SiC

We present a comprehensive study on metal-organic vapor phase epitaxy growth of N-polar and Al -polar AlN on 4H-SiC with 4° miscut using constant growth parameters. At a high temperature of 1165 °C, N-polar AlN layers had high crystalline quality whereas the Al-polar AlN surfaces had a high density of etch pits. For N-polar AlN, the V/III ratio below 1000 forms hexagonal hillocks, while the V/III ratio over 1000 yields step bunching without the hillocks. 1-μm-thick N-polar AlN layer grown in optimal conditions exhibited FWHMs of 307, 330 and 337 arcsec for (0 0 2), (1 0 2) and (2 0 1) reflections, respectively.

Growth and characterization of Piperine (PPN) single crystal grown by slow evaporation solution growth technique

An organic single crystal Piperine (PPN) was grown by slow evaporation solution growth technique (SEST). Single crystal X-ray diffraction measurements were carried out on grown piperine single crystals. The crystal system was identified and lattice parameters were measured from the powder X-ray diffraction (PXRD) measurement. The transmittance of the grown crystal and cut off wavelength were analysed using UV–vis NIR studies and the cut-off wavelength was found to be 387 nm. Vickers micro hardness analysis was carried out to identify the mechanical stability of the grown crystal. Chemical etching study was carried out using different etchants and the etch pit density (EPD) was calculated. The third order nonlinear optical property of PPN crystal was studied using Z-scan technique with He–Ne laser (632·8 nm).

Halide-oxide carbon vapor transport of ZnO: Novel approach for unseeded growth of single crystals with controllable growth direction

The thermodynamic analysis of using HCl + CO gas mixture as a chemical vapor transport agent (TA) for ZnO single crystal growth in closed ampoules, including 11 chemical species, is carried out for wide temperature and loaded TA pressure ranges. The advantages of HCl + CO TA for faster and more stable growth are shown theoretically in comparison with HCl, HCl + H2 and CO. The influence of the growth temperature, of the TA density, of the HCl/CO ratio, and of the undercooling on the ZnO mass transport rate was investigated theoretically and experimentally. The HCl/CO ratios favorable for the growth of m planes and (0001)Zn surface were found. It was shown that HCl + CO TA provides: (i) a rather high growth rate (up to 1.5 mm per day); (ii) a decrease of wall adhesion effect and an etch pit density down to 103 cm−2; (iii) a minimization of growth nucleus quantity down to 1; (iv) stable unseeded growth of the high crystalline quality large single crystals with a controllable preferred growth direction. The characterization by the photoluminescence spectra, the transmission spectra and the electrical properties are analyzed.

Guidelines for establishing an etching procedure for dislocation density measurements on multicrystalline silicon samples

With multicrystalline silicon becoming the main material used for photovoltaic applications and dislocations being one of the main material limitations to better solar cell efficiency, etch pit density measurements are gaining more importance. Traditionally, etch pit density measurements are based on selective etching of silicon samples. The majority of the etchants have been developed for monocrystalline samples with known orientation, while those developed for multicrystalline samples have been less investigated and might need some optimization. In this study, we use and compare the PVScan tool, which provides a quick way to assess dislocation density on selectively etched samples, and microscope image analysis. We show how the etching methods used for dislocation density measurements can affect the results, and we suggest how to optimize the Sopori etching procedure for multicrystalline silicon samples with high dislocation densities. We also show how the Sopori etchant can be used to substitute Secco while maintaining a high precision of dislocation density measurements, but without the toxic hexavalent chromium compounds.

Growth and characterization of semi-organic nonlinear optical (NLO) guanidinium trichloroacetate (GTCA) single crystal

The semi-organic nonlinear optical single crystal of guanidinium trichloroacetate (GTCA) was grown by slow evaporation solution technique. The grown crystal was subjected to single crystal XRD studies to confirm the lattice parameters. Fourier transform infrared (FTIR) analysis was carried out to identify the functional groups of the grown crystal. The UV–vis NIR spectrum was carried out and the calculated band gap energy was found to be 4.72eV. The thermal behavior of the grown crystal was analyzed by thermal gravimetric-differential thermal analysis (TG-DTA). This shows that there are no weight losses upto 160°C. The photoconductivity study reveals that the grown crystal has negative photoconductive nature. Vickers microhardness analysis was carried out to identify the mechanical stability of the grown crystal. Chemical etching study was carried out using water etchant and the etch pit density (EPD) was calculated. The electronic polarizability was calculated from the solid state dielectric related parameters such as valence electron, plasma energy, Penn gap and Fermi energy for the GTCA using the empirical relation. These estimated values were utilized to report the electronic polarizability. It well matches to the value calculated from Clausius-Mossotti relation and optical band gap energy. The Kurtz-Perry powder technique was used to analyze second harmonic generation (SHG) efficiency of the grown crystal.

Control wafer bow of InGaP on 200 mm Si by strain engineering

When epitaxially growing III–V compound semiconductors on Si substrates the mismatch of coefficients of thermal expansion (CTEs) between III–V and Si causes stress and wafer bow. The wafer bow is deleterious for some wafer-scale processing especially when the wafer size is large. Strain engineering was applied in the epitaxy of InGaP films on 200 mm silicon wafers having high quality germanium buffers. By applying compressive strain in the InGaP films to compensate the tensile strain induced by CTE mismatch, wafer bow was decreased from about 100 μm to less than 50 μm. X-ray diffraction studies show a clear trend between the decrease of wafer bow and the compensation of CTE mismatch induced tensile strain in the InGaP layers. In addition, the anisotropic strain relaxation in InGaP films resulted in anisotropic wafer bow along two perpendicular (110) directions. Etch pit density and plane-view transmission electron microscopy characterizations indicate that threading dislocation densities did not change significantly due to the lattice-mismatch applied in the InGaP films. This study shows that strain engineering is an effective method to control wafer bow when growing III–V semiconductors on large size Si substrates.

85% internal quantum efficiency of 280-nm AlGaN multiple quantum wells by defect engineering

In this study, high internal-quantum-efficiency (IQE) AlGaN multiple quantum wells (MQWs) were successfully demonstrated on low-defect-density AlN templates with nano-patterned sapphire substrates. These templates consisted of AlN structures with 0∼30 periods superlattices (SLs) by alternating high (100) and low (25) V/III ratios under a low growth temperature (1130 °C). Compared to conventional high crystal-quality AlN epilayers achieved at temperatures ≥1300 °C, lower thermal budget can reduce the production cost and wafer warpage. Via optimization of the SL period, the AlN crystallinity was systematically improved. Strong dependence of SL period number on the X-ray full-width-at-half-maximum (FWHM) of the AlN epilayer was observed. The AlN template with 20-period SLs exhibited the lowest FWHM values for (0002) and (10ī2), namely 331 and 652 arcsec, respectively, as well as an ultra-low etching pit density of 1 × 105 cm−2. The relative IQE of 280 nm AlGaN MQWs exhibited a dramatically increase from 22.8% to 85% when the inserted SL increased from 0 to 20 periods. It has hardly ever been reported for the AlGaN MQW sample. The results indicate that the engineered AlN templates have high potential applications in deep ultraviolet light emitters.

Bulk growth of organic 4-hydroxy l-proline (HLP) single crystals grown by conventional slow evaporation and Sankaranarayanan–Ramasamy (SR) method

Organic single crystals of 4-hydroxy l-proline (HLP) were grown by conventional slow evaporation and Sankaranarayanan–Ramasamy (SR) method in an aqueous medium. With a vision to improve the crystal quality, SR method was adopted and optically transparent HLP single crystal, (110) directed, with the size of 80 mm length and 15 mm diameter was grown. The crystalline structure of the grown crystal was analyzed by single crystal X-ray diffraction (SXRD) analysis. The conventional and SR method grown HLP crystals were characterized and the results were compared by UV–Vis–NIR, photoluminescence, chemical etching, Vickers microhardness, dielectric permittivity, dielectric loss, photoconductivity, photoacoustic, laser damage threshold (LDT) and second harmonic generation (SHG) measurements. The thermal property of the grown crystal was carried out by thermogravimetric (TG) and differential thermal analysis (DTA). The SHG efficiency of HLP crystal was determined using Kurtz–Perry powder technique. The comparative optical transmittance study clearly indicates that the transmission of SR method grown HLP crystal is 10% higher and quite good in the entire visible and near infrared region which suggest its suitability for optical device applications. The distribution of structural defects and the etch pit density (EPD) of the grown crystals were determined by chemical etching analysis. The Vickers microhardness measurement reveals that the hardness of SR method grown HLP crystal is higher compared to conventional method grown crystal. The dielectrics, photoconductivity, photoacoustic and laser damage threshold studies clearly indicate that the crystal grown by SR method possesses good quality compared to conventional method grown crystal.

Correlation of Etch Pits and Dislocations in As-grown and Thermal-Cycle-Annealed HgCdTe(211) Films

This paper reports observations of the different types of etch pits and dislocations present in thick HgCdTe (211) layers grown by molecular beam epitaxy on CdTe/Si (211) composite substrates. Dislocation analysis for as-grown and thermal cycle-annealed samples has been carried out using bright-field transmission electron microscopy. Triangular pits present in as-grown material are associated with a mixture of Frank partials and perfect dislocations, while pits with fish-eye shapes have perfect dislocations with $$ \frac{1}{2}[0\bar{1}1] $$ Burgers vector. The dislocations beneath skew pits are more complex as they have two different crystallographic directions, and are associated with a mixture of Shockley partials and perfect dislocations. Dislocation analysis of samples after thermal cycle annealing (TCA) shows that the majority of dislocations under the etch pits are short segments of perfect dislocations with $$ \frac{1}{2}[0\bar{1}1] $$ Burgers vector while the remainder are Shockley partials. The absence of fish-eye shape pits in TCA samples suggests that they are associated with mobile dislocations that have reacted during annealing, causing the overall etch pit density to be reduced. Very large pits with a density ∼2×103 cm−2 are observed in as-grown and TCA samples. These defects thread from within the CdTe buffer layer into the upper regions of the HgCdTe layers. Their depth in as-grown material is so large that it is not possible to locate and identify the underlying defects.

Metalorganic vapor phase epitaxy of AlN on sapphire with low etch pit density

Using metalorganic vapor phase epitaxy, methods were developed to achieve AlN films on sapphire with low etch pit density (EPD). Key to this achievement was using the same AlN growth recipe and only varying the pre-growth conditioning of the quartz-ware. After AlN growth, the quartz-ware was removed from the growth chamber and either exposed to room air or moved into the N2 purged glove box and exposed to H2O vapor. After the quartz-ware was exposed to room air or H2O, the AlN film growth was found to be more reproducible, resulting in films with (0002) and (10–12) x-ray diffraction (XRD) rocking curve linewidths of 200 and 500 arc sec, respectively, and EPDs < 100 cm−2. The EPD was found to correlate with (0002) linewidths, suggesting that the etch pits are associated with open core screw dislocations similar to GaN films. Once reproducible AlN conditions were established using the H2O pre-treatment, it was found that even small doses of trimethylaluminum (TMAl)/NH3 on the quartz-ware surfaces generated AlN films with higher EPDs. The presence of these residual TMAl/NH3-derived coatings in metalorganic vapor phase epitaxy (MOVPE) systems and their impact on the sapphire surface during heating might explain why reproducible growth of AlN on sapphire is difficult.

Crystal growth and characterization of third order nonlinear optical piperazinium bis(4-hydroxybenzenesulphonate) (P4HBS) single crystal

The organic single crystal of piperazinium bis(4-hydroxybenzenesulphonate) (P4HBS) was grown by slow evaporation solution technique (SEST) at room temperature. The lattice parameters of the grown crystal were confirmed by single crystal X-ray diffraction analysis. Functional groups of P4HBS crystal were confirmed by FTIR spectrum analysis. The optical quality of the grown crystal was identified by the UV–Vis NIR spectrum analysis. The grown crystal has good optical transmittance in the range of 410–1100nm. In photoluminescence spectrum, sharp emission peaks are observed, which indicates the ultraviolet (UV) emission. The photoconductivity study reveals that the grown crystal has negative photoconductive nature. The thermal behaviour of the P4HBS crystal was investigated by thermogravimetric and differential thermal analysis (TG-DTA). The mechanical stability of grown crystal was analyzed and the indentation size effect (ISE) was explained by Hays-Kendall’s (HK) approach and proportional specimen resistance model (PSRM). Chemical etching study was carried out and the etch pit density (EPD) was calculated. The dielectric constant (ε′) and dielectric loss (tan δ) as a function of frequency were measured for the grown crystal. The solid state parameters such as valence electron, plasma energy, Penn gap and Fermi energy were evaluated theoretically for the P4HBS using the empirical relation. The estimated values are used to calculate the electronic polarizability. The third-order nonlinear optical properties such as nonlinear refractive index (n2), absorption co-efficient (β) and susceptibility (χ(3)) were studied by Z-scan technique at 632.8nm using He-Ne laser.

Industrial growth and characterization of Si‐doped GaAs crystal by a novel multi‐crucible Bridgman method

In this wok, a novel multi‐crucible Bridgman method is developed to produce the Ø 2 inch Si‐doped GaAs crystals. Five placements are designed in the furnace means five ingots could be produced at the same time. Twinning and high dislocation density are the main growth defects that often take place in the crystals. After the solid‐liquid interface and crystal cooling rate are optimized, the Si‐doped GaAs crystals with favorable single crystalline yield are successfully obtained. The average etching pits density (EPD) of optimized GaAs crystals is <1500/cm2. Full width at half maximum (FWHM) are tested all less than 60″ that indicates GaAs crystals have high crystalline quality. The carrier concentration near the bottom and tail parts of ingots is in range of (4.5‐5.9) × 1017 /cm3 and (1.2‐2.1) × 1018 /cm3 due to segregation of Si element in GaAs crystals. Accordingly, the mobility is decreased from 2128–2651 cm2/v.s to 1581–1854 cm2/v.s. The result proves such multi‐crucible Bridgman method is a feasible way for industrial growth of Si‐doped GaAs crystals for opto‐electronic application.