Jesudoss Arokiaraj

High-Density Plasma Enhanced Quantum Well Intermixing in InGaAs/InGaAsP Structure Using Argon Plasma

Photoluminescence was used to study the band-gap shift of argon (Ar) plasma induced quantum well intermixing in InGaAs/InGaAsP laser structure. Ar exposure for 5 min and subsequent annealing resulted in maximum blue shift of 61.4 meV. This is the first time to use the high-density plasma enhanced intermixing technique developed in inductively coupled plasma (ICP) machine to demonstrate the result of bandgap blue-shift with the improvement of crystalline quality as compared to plasma generated from pure RF power. This technique provides a promising approach of bandgap tuning for photonic integrated circuits (PIC), which demand high crystalline quality.

High-quality GaAs on Si substrate by the epitaxial lift-off technique using SeS2

In this letter, we demonstrate the realization of strong bonding between GaAs epilayers on Si substrates by using selenium sulphide (SeS2) compound. After bonding, the sample has been transplanted to Si substrate using the epitaxial lift-off process. Such a transplanted film was found to be very smooth and adhered well to Si. The resulting chemical bond was covalent in nature, robust, and withstood clean room processing steps. The film bonded in this manner exhibited very good photoluminescence and high crystal quality by double crystal x-ray diffraction. The double crystal x-ray diffraction had a low full width at half maximum of 44 arcsec, and the strain was absent in these types of heterostructures. The interfacial chemical reaction and bonding were studied by depth profile x-ray photoelectron spectroscopy. It was concluded that Ga–Se and Si–S phases such as Ga2Se3 and SiS2 were responsible for the strong bonding between GaAs and Si.

Growth of stress-released GaAs on GaAs/Si structure by metalorganic chemical vapor deposition

A stress-released GaAs layer was grown on GaAs bonded to Si substrate with the combination of epitaxial lift-off technique and regrowth by metalorganic chemical vapor deposition. The GaAs thin film was bonded to Si substrate using SeS2 and another GaAs layer was regrown. The photoluminescence peak wavelength and the slope of the time resolved photoluminescence decay of GaAs/Si are almost the same as those of GaAs grown on GaAs substrate.

Electrical Characteristics of GaAs Bonded to Si Using SeS2 Technique

We have developed a new technique for bonding GaAs on Si susbtrates; called surface modification by chemical treatment. The treatment of selenium sulphide (SeS2) with GaAs produces a reconstructed surface which helps in strong fusion between GaAs and Si at lower temperatures and without weights. The current–voltage (I–V) characteristics of both n-GaAs/n-Si and p-GaAs/p-Si were measured at room temperature. The I–V curve did not show a rectifying behaviour when GaAs was bonded to Si with SeS2 because of the formation of a high-resistance layer at the interface. The characteristics were greatly improved by small additions of Sn to SeS2 during the bonding process. Sn forms localized islands in addition to the Ga–Se and Se–S, and acts as shunt resistance between GaAs and Si.

Characterization of GaAs PN junction bonded on selenium sulphide (SeS/sub 2/) treated Si substrates

Thin-film epitaxial GaAs grown by metal-organic chemical vapor deposition (MOCVD) have been successfully lifted-off from the original GaAs substrate using the epitaxial lift-off (ELO) technique and robustly bonded to selenium sulphide treated silicon substrates without deteriorating the electrical, optical and structural properties of the device. The bonding is a low temperature process and the bonding mechanism is based on the surface reconstruction of the two semiconductors placed in contact. Nomarski surface contrast microscopy reveals that the surface is smooth and uniform after transplantation. Optical properties exhibited good characteristics without stress in the grafted films. The selenium sulphide treated Si substrate is transparent to light and the solar cell exhibits an efficiency of 5.5%.

Surface and Bulk Passivation effect of GaAs grown on Si Substrates by SeS2Treatment

The effect of selenium sulphide (SeS2) treatment for GaAs grown on Si has been studied. The surface and bulk properties such as the photoluminscence intensity and minority carrier life-time have been significantly increased. The PL intensity showed a two fold and four fold increase for the as-passivated, passivated and annealed samples. It is proposed that the passivation on the surface occurs by means of sulphur and selenium atoms. The bulk passivation is by means of diffusion of Se into the bulk of the epilayer. Additional steps of annealing increased the minority carrier life time thereby reducing the recombination velocity and also indiffusion of Se helps to passivate the buried defects such as AsGa in the double heterostructures. Results obtained by X-ray photoelectron spectroscopy (XPS) reveal that sulfides and selenides reside on the outermost surface and only gallium based selenides are in the bulk of the GaAs layer.

INVESTIGATIONS OF A RAPID THERMAL ANNEALED AL0.15GA0.85AS/SI STRUCTURE

Al0.15Ga0.85As/Si grown by metalorganic chemical vapor deposition (MOCVD) was subjected to rapid thermal annealing (RTA) and investigated by photoluminescence (PL), scanning electron microscopy (SEM), Auger electron spectroscopy (AES), secondary ion mass spectrometry (SIMS) and double crystal X-ray diffraction (XRD) measurements. After RTA at 850°C for 10 s the PL intensity increased significantly. Above 900°C, quenching of PL intensity was observed. An emission at 1.515 eV was observed only in 900 and 950°C annealed samples and is attributed to the formation of a Si-related complex defect. AES and SIMS measurements revealed the diffusion of Si at higher annealing temperatures from the top surface into the epilayer and this diffusion is accounted for by a gas phase reaction. Double-crystal XRD showed a decreasing full width at half maximum (FWHM) value as the annealing temperature was increased.

Phosphine-added hydrogen plasma passivation of GaAs solar cell on Si substrate

The improvement of the GaAs solar cell on Si substrate (GaAs/Si solar cell) has been studied by treating phosphine-added hydrogen plasma (PH/sub 3//H/sub 2/ plasma) exposure. Phosphidization of GaAs surface and defect-passivation of entire GaAs bulk layer are realized simultaneously. As a result, surface recombination states are reduced, and the minority carrier lifetime is increased. Furthermore, the reduction of interface (GaAs/AlGaAs) recombination velocity is confirmed. For PH/sub 3//H/sub 2/ plasma exposed GaAs/Si solar cell, high open-circuit voltage and fill factor are obtained. Consequently, the conversion efficiency is increased from 15.9% to 18.6%.

SeS2 assisted bonding of GaAs to Si–A new method for wafer bonding

A new technique namely chemical bonding by surface modification (CBSM) has been developed to bond GaAs thin films on Si substrate. The bonded GaAs epilayer, detached from its orginal substrate in conjunction with epitaxial lift-off (ELO) process, possessed smooth surface morphology and exhibited uniform bonding across the interface. The X-ray full width at half maximum (FWHM) of 16 arc-sec from double crystal X-ray diffraction (DCD) and no peak wavelength shift from photoluminscence (PL) measurements reflected the high crystalline quality of the bonded films. The depth profile by XPS revealed at the interface the occurrence of surface modification. The surface modification resulted in the formation of Ga2Se3 and SiS2, which attributed for the strong and high quality bonding between GaAs and Si.

Optical and Structural Quality of GaAs Epilayers from Gallium, Bismuth Mixed Solvents by Liquid Phase Epitaxy

Liquid phase epitaxy (LPE) of GaAs epilayers grown at 645°C was studied for different Bi compositions in Ga solvent . Mixed solvents such as Ga+Bi were used to improve GaAs epilayer quality. The grown layers were characterized by photoluminescence (PL) and etch pit density (EPD) measurements. The Bi composition was varied from 0 to 100% in Ga. Good quality epilayers were obtained for 100% Bi composition. PL investigations revealed that the epilayer grown using equal atomic percentage of Ga and Bi had good crystallinity, which is comparable with the 100%-Ga-grown epilayer. The PL measurements reveal that carbon inclusion in the epilayer grown using 50% Ga and 50% Bi solution is comparably less than other solvent compositions. The EPD was reduced to more than half order of magnitude when the solvent was changed from Ga to Bi. The EPD results of epilayers grown using mixed solvents are reported for the first time. The EPD of the GaAs epilayer grown using 50% Ga and 50% Bi solution is markedly reduced compared to the other Ga+Bi mixed solvents, and it is almost equal to the EPD of 100%-Bi-grown epilayers.