Improvement of the performance of GaN-based LEDs grown on sapphire substrates patterned by wet and ICP etching

Sapphire substrates patterned by a selective chemical wet and an inductively coupled plasma (ICP) etching technique was proposed to improve the performance of GaN-based light-emitting diodes (LEDs). GaN-based LEDs were fabricated on sapphire substrates through metal organic chemical vapor deposition (MOCVD). The LEDs fabricated on the patterned substrates exhibit improved device performance compared with the conventional LED fabricated on planar substrates when growth and device fabricating conditions were the same. The light output powers of the LEDs fabricated on wet-patterned and ICP-patterned substrates were about 37% and 17% higher than that of LEDs on planar substrates at an injection current of 20 mA, respectively. The enhancement is attributable to the combination of the improvement of GaN-based epilayers quality and the improvement of the light extraction efficiency. (c) 2008 Elsevier Ltd. All rights reserved.

Fabrication of nano-patterned sapphire substrates and their application to the improvement of the performance of GaN-based LEDs

Nano-patterned sapphire substrates (NPSSs) were fabricated by a chemical wet etching technology using nano-sized SiO2 as masks. The NPSS was applied to improve the performance of GaN-based light emitting diodes (LEDs). GaN-based LEDs on NPSSs were grown by metal organic chemical vapour deposition. The characteristics of LEDs grown on NPSSs and conventional planar sapphire substrates were studied. The light output powers of the LEDs fabricated on NPSSs were considerably enhanced compared with that of the conventional LEDs grown on planar sapphire substrates.

Radiation hardness improvement of separation-by-implantation-of-oxygen/silicon-on-insulator material by nitrogen ion implantation

In our work, nitrogen ions were implanted into separation-by-implantation-of-oxygen (SIMOX) wafers to improve the radiation hardness of the SIMOX material. The experiments of secondary ion mass spectroscopy (SIMS) analysis showed that some nitrogen ions were distributed in the buried oxide layers and some others were collected at the Si/SiO2 interface after annealing. The results of electron paramagnetic resonance (EPR) suggested the density of the defects in the nitrided samples changed with different nitrogen ion implantation energies. Semiconductor-insulator-semiconductor (SIS) capacitors were made on the materials, and capacitance-voltage (C-V) measurements were carried out to confirm the results. The super total dose radiation tolerance of the materials was verified by the small increase of the drain leakage current of the metal-oxide-semiconductor field effect transistor with n-channel (NMOSFETs) fabricated on the materials before and after total dose irradiation. The optimum implantation energy was also determined.

Improvement of the radiation hardness of SIMOX buried layers using nitrogen implantation

An investigation of hardening the buried oxides (BOX) in separation by implanted oxygen (SIMOX) silicon-on-insulator (SOI) wafers to total-dose irradiation has been made by implanting nitrogen into the BOX layers with a constant dose at different implantation energies. The total-dose radiation hardness of the BOX layers is characterized by the high frequency capacitance-voltage (C-V) technique. The experimental results show that the implantation of nitrogen into the BOX layers can increase the BOX hardness to total-dose irradiation. Particularly, the implantation energy of nitrogen ions plays an important role in improving the radiation hardness of the BOX layers. The optimized implantation energy being used for a nitrogen dose, the hardness of BOX can be considerably improved. In addition, the C-V results show that there are differences between the BOX capacitances due to the different nitrogen implantation energies.

Performance improvement of GaN based Schottky barrier ultraviolet photodetector by adding a thin AlGaN window layer

We propose a new structure of GaN based Schottky barrier ultraviolet photodetector, in which a thin n-type AlGaN window layer is added on the conventional n(-)-GaN/n(+)-GaN device structure. The performance of the Schottky barrier ultraviolet photodetector is found to be improved by the new structure. The simulation result shows that the new structure can reduce the negative effect of surface states on the performance of Schottky barrier GaN photodetectors, improving the quantum efficiency and decreasing the dark current. The investigations suggest that the new photodetector can exhibit a better responsivity by choosing a suitably high carrier concentration and thin thickness for the AlGaN window layer.

Quality improvement of GaInNAs/GaAs quantum wells grown by plasma-assisted molecular beam epitaxy

The optimum growth condition of GaInNAs/GaAs quantum wells (QWs) by plasma-assisted molecular beam epitaxy was investigated. High-resolution X-ray diffraction and photoluminescence (PL) measurements showed that ion damage drastically degraded the quality of GaNAs and GaInNAs QWs and that ion removal magnets can effectively remove the excess ion damage. Remarkable improvement of PL intensity and obvious appearance of pendellosung fringes were observed by removing the N ions produced in the plasma cell. When the growth rate increased from 0.73 to 1.2 ML/s, the optimum growth temperature was raised from 460 degreesC to 480 degreesC and PL peak intensity increased two times. Although the N composition decreased with increasing growth rate, degradation of optical properties of GaInNAs QWs was observed when the growth rate was over 0.92 ML/s. Due to low-temperature growth of GaInNAs QWs, a distinctive reflection high-energy electron diffraction pattern was observed only when the GaAs barrier was grown under lower As-4 pressure. The samples with GaAs barriers grown under lower As-4 pressure (V/III ratio about 24) exhibited seven times increase in PL peak intensity compared with those grown under higher As-4 pressure (V/III ratio about 50). (C) 2001 Elsevier Science B,V. All rights reserved.

Improvement of thin silicon on sapphire (SOS) film materials and device performances by solid phase epitaxy

The increased emphasis on sub-micron CMOS/SOS devices has placed a demand for high quality thin silicon on sapphire (SOS) films with thickness of the order 100-200 nm. It is demonstrated that the crystalline quality of as-grown thin SOS films by the CVD method can be greatly improved by solid phase epitaxy (SPE) process: implantation of self-silicon ions and subsequent thermal annealing. Subsequent regrowth of this amorphous layer leads to a greater improvement in silicon layer crystallinity and channel carrier mobility, evidenced, respectively, by double crystal X-ray diffraction and electrical measurements. We concluded that the thin SPE SOS films are suitable for application to high-performance CMOS circuitry. (C) 2000 Elsevier Science S.A. All rights reserved.

Improvement of photoluminescence of strained SiGe/Si layers on patterned Si substrate

A strained SiGe/Si superlattice structure has been grown on a patterned Si substrate and its photoluminescence has been studied. The patterned substrate is composed of pyramid-like structures. It is found that there are Ge-rich SiGe quantum wires (QWR) at the crossings of adjacent planes that form the pyramid-like structure. Photoluminescence of strained the SiGe layer grown on a planar substrate and a patterned substrate was compared. The total intensity of photoluminescence from the patterned substrate was 5.2 times larger than that from the planar substrates. The result is discussed and it is believed that this increase in photoluminescence is related to the observed QWRs. (C) 1999 Elsevier Science Ltd. All rights reserved.

Improvement of the photoluminescence from gallium nitride layers grown by MBE with an additional incident indium flux

The effect of using an indium flux during the MBE growth of GaN layers was investigated. The properties of these layers were studied using electron probe microanalysis, secondary ion mass spectroscopy, photoluminescence and cathodoluminescence. The optical properties of the GaN layers are shown to improve as compared with undoped GaN layers grown under nominally the same conditions but without an additional indium flux.

Improvement of stoichiometry in semi-insulating gallium arsenide grown under microgravity

A semi-insulating (SI) GaAs single crystal was recently grown in a retrievable satellite. The average etch pit density (EPD) of dislocations in the crystal revealed by molten KOH is 2.0 x 10(4) cm(-2), and the highest EPD is 3.1 x 10(4) cm(-2) This result indicates a quite good homogenity of the EPD which is much better than the ground-grown crystals. A similar better homogenity of the stoichiometry i.e., the [As]/([As] + [Ga]) ratio has been found in the space-grown SI-GaAs single crystal studied nondestructively using a new mapping method based upon X-ray Bond diffraction. The average stoichiometry in the space-grown crystal is 0.50007 with mean-square deviation of 6x10(-6), while the average stoichiometry in ground-grown SI-GaAs crystal is more than 0.50010. (C) 1998 Elsevier Science B.V. All rights reserved.

Stability improvement of selective oxidation during the fabrication of InGaAs/GaAs vertical cavity surface emitting laser

The effects of the carrier gas flow and water temperature on the oxidation rate for different reaction temperatures were investigated. The optimum conditions for stable oxidation were obtained. Two mechanisms of the oxidation process are revealed. One is the flow-controlling process, which is unstable. The other is the temperature-controlling process, which is stable. The stable region decreases for higher reaction temperatures. The simulation results for the stable oxidation region are also given. With optimum oxidation conditions, the stability and precision of the oxidation can be dramatically improved.

Improvement of Ge self-organized quantum dots by use of Sb surfactant

A Sb-mediated growth technique is developed to deposit Ge quantum dots (QDs) of small size, high density, and foe of dislocations. These QDs were grown at low growth temperature by molecular beam epitaxy. The photoluminescence and absorption properties of these Ge QDs suggest an indirect-to-direct conversion, which is in good agreement with a theoretical calculation. (C) 1998 American Institute of Physics. [S0003-6951(98)00420-3].

Improvement of GaN-based light emitting diodes performance grown on sapphire substrates patterned by wet etching - art. no. 684107

An effective approach to enhance the light output power of InGaN/GaN light emitting diodes (LED) was proposed using pyramidal patterned sapphire substrates (PSS). The sapphire substrates were patterned by a selective chemical wet etching technique. GaN-based LEDs were fabricated on patterned sapphire substrates through metal organic chemical deposition (MOCVD). The LEDs fabricated on patterned sapphire substrates exhibit excellent device performance compared to the conventional LEDs fabricated on planar sapphire substrates in the case of the same growth and device fabricating conditions. The light output power of the LEDs fabricated on patterned sapphire substrates was about 37% higher than that of LEDs on planar sapphire substrates at an injection current of 20 mA. The significant enhancement is attributable to the improvement of the quality of GaN-based epilayers and improvement of the light extraction efficiency by patterned sapphire substrates.

The improvement of thick oxidized porous silicon layer growth process - art. no. 60290S

Oxidizing thick porous silicon layer into silicon dioxide is a timesaving and low-cost process for producing thick silicon dioxide layer used in silicon-based optical waveguide devices. The solution of H2O2 is proposed to post-treat thick porous silicon (PS) films. The prepared PS layer as the cathode is applied about 10 mA/cm(2) current in mixture of ethanol, HF, and H2O2 solutions, in order to improve the stability and the smoothness of the surface. With the low-temperature dry-O-2 pre-oxidizations and high-temperature wet O-2 oxidizations process, a high-quality SiO2 30 mu m thickness layer that fit for the optical waveguide device was prepared. The SEM images show significant improved smoothness on the surface of oxidized PS thick films, the SiO2 film has a stable and uniformity reflex index that measured by the prism coupler, the uniformity of the reflex index in different place of the wafer is about 0.0003.

Improvement of the electrical property of semi-insulating InP by suppression of compensation defects

Semi-insulating (SI) InP obtained by iron phosphide ambient annealing has very low concentration of deep level defects and better electrical property than SI-InP annealed in phosphorus ambient. The defect suppression phenomenon correlates with Fe diffusion and substitution in the annealing process. Analysis of the experimental result suggests that a high activation ratio of incorporated Fe in InP has an effect of defect suppression in Fe-doped and Fe-diffused SI-InP.