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ABSTRACT: Purpose – The purpose of this paper is to describe a very low-cost way to prepare Ge nano/microstructures by means of filling the material inside porous silicon (PS) using a conventional and cost effective technique in which thermal evaporator with PS acts as patterned substrate. Also, the potential metal-semiconductor-metal (MSM) photodetector IV characteristics of the structure are demonstrated. Design/methodology/approach – PS was prepared by anodization of Si wafer in ethanoic hydrofluoric acid. The Ge layer was then deposited onto the PS by thermal evaporation. The process was completed by Ni metal deposition using thermal evaporator followed by metal annealing of 400°C for 10?min. Structural analysis of the samples was performed using energy dispersive X-ray analysis (EDX), scanning electron microscope (SEM), X-ray diffraction (XRD) and Raman spectroscopy. Findings – A uniform circular network distribution of pores is observed with sizes estimation of 100?nm to 2.5?µm by SEM. Also observed are clusters with near spherical shape clinging around the pores believed to be Ge or GeO2. The EDX spectrum suggests the presence of Ge or GeO2 on and inside the pore structure. Raman spectrum showed that good crystalline structure of the Ge can be produced inside the silicon pores. XRD showed the presence of a Ge phase with the diamond structure by (111), (220), and (400) reflections. Finally, current-voltage (I-V) measurement of the Si/Ge/PS MSM photodetector was carried out. It showed lower dark currents compared to control device of Si. The device showed enhanced current gain compared to conventional Si device which can be associated with the presence of Ge nanostructures in the PS. Originality/value – This paper shows that it is possible to grow Ge nano/microstructure on PS by using a simple and low-cost method of thermal evaporation and thermal annealing and demonstrates potential MSM photodetector IV characteristics from the device.
Microelectronics International 08/2010; 27(3):154-158. · 0.60 Impact Factor
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ABSTRACT: In this paper we presented an efficient polarization rotator (PR) based on multiple slots slanted silica waveguide. The design comprised of three layers of high index contrast (∼2%) germanium doped silica waveguide, with a slant angle of 45°. An efficient and practical design was obtained with an overall length of about 2.6 mm and its power transfer efficiency of about 90% with the input∕output waveguides. The polarization conversion achieved is about 98% with an extinction ratio of ‐26 dB at a wavelength of 1.55 μm. The PR response is also relatively stable with respect to variation in the operating wavelength. The analysis of the PR waveguide was conducted using finite element—eigenmode expansion (FE‐EME) method.
AIP Conference Proceedings. 07/2010; 1250(1):141-144.
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ABSTRACT: Porous silicon was prepared by using an argon-ion laser in a laser-induced etching process with different etching time. Scanning electron microscopy was used to monitor changes in surface morphology produced during the etching process. Porous silicon samples were subjected to spectroscopic investigations. The first-order Raman line asymmetry was found to decrease with increase of the etching time, while the peak position downshifted for a given power density. The photoluminescence spectra (PL) exhibit a blue shift in peak position with etching time. Both Raman and PL data were explained using appropriate quantum confinement models involving three-dimensional confinement and Gaussian size distributions of nanocrystallites constituting porous silicon samples. There is reasonable agreement between the results obtained from Raman and PL spectroscopic investigations of the PS samples.
JOAM. 11/2008; 10:2653-2656.
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ABSTRACT: Porous GaAs was formed by electrochemical etching of n-type GaAs wafers in HF- or HCl-based solution with different current densities. The porous structure formation has been confirmed by scanning electron microscopy and x-ray diffraction. The samples were subjected to Raman and photoluminescence (PL) spectroscopic investigations. Our results show that the spontaneous emission is originated from extremely small structures. As the porosity increases, there is an increase of the luminescent peak, lower energy shifting of the Raman feature, exhibiting broadening and decreased of first-order longitudinal optic mode peak intensity. In addition, the intensity of the transverse optic (TO) mode was highly enhanced and its peak was broadened due to the breakdown of the polarization selection rule in the case of high-porosity samples. Two new peaks around 200 and 233 cm−1 were observed, which were attributed to α-As and TO-Ga-As-a respectively. Both Raman and PL results were explained using quantum confinement models. There is reasonable agreement between the results obtained from PL and Raman spectroscopic investigations of the etched GaAs samples.
Semiconductor Science and Technology 04/2008; 23(5):055016. · 1.72 Impact Factor
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ABSTRACT: In this paper we used new microcavity resonator design of extracting light with high efficiency from a high index material (GaN), n > 2 for use in light emitting diode (LED) and laser diode (LD). A GaN/sapphire structure as an active layer was sandwiched between two silver mirrors. For the study two types of microcavity were fabricated: (air/GaN/sapphire/silver) and (silver/GaN/sapphire/silver). Via photo-luminescence measurements we observed 2-fold intensity enhancement in the UV region (364 nm) at room temperature by using 400 nm silver back mirror compared with uncoated sample. The amplitude of the photoluminescence is enhanced 10-times when we used 400 nm back coated together with 50 nm silver as front mirror. Further, a tremendous enhancement was obtained when a small hole was made in the front mirror with 50 nm thickness. The large increment of GaN/sapphire light emission in this microcavity could be caused by few important factors: increasing absorption in the cavity, optical field enhancement due to the resonator and coupling of plasmon in the metallic layer with the UV light. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
physica status solidi (c) 05/2006; 3(6):2022 - 2025.
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ABSTRACT: The performance of GaN/AlGaN quantum well was simulated using ATLAS software (Silvaco International Inc.). In this work, we simulated a quantum well active region of GaN with AlGaN cladding layers. Here, we studied the changes in radiative efficiency with the thickness of the active layer from 3 nm to 90 nm and found that the radiative efficiency increases when the thickness of the active layer was increased. We also found that the relative positions of the conduction band for GaN and n-type AlGaN vary beyond our expectation when the thickness of the active region is over 75 nm
Semiconductor Electronics, 2004. ICSE 2004. IEEE International Conference on; 01/2005
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ABSTRACT: In this paper, we investigated the effect of reactive hydrogen plasma, used in the thermal cleaning process of the substrate, on the optical properties of gallium nitride (GaN) films deposited on c-plane sapphire substrates in the reststrahlen and near bandgap regions. The GaN films were grown at 700 C by plasma-assisted metal organic chemical vapour deposition. IR reflectance and absorption measurements were conducted to study the optical properties in the reststrahlen and near bandgap region respectively. Since the optical properties of a material greatly depend on its structural properties, X-ray diffraction (XRD) and atomic force microscopy (AFM) measurements were also performed as a comparison to the optical results. In addition, Hall effect measurements using the van der Pauw configuration were conducted to obtain the carrier density and mobility of the GaN films.
Semiconductor Electronics, 2004. ICSE 2004. IEEE International Conference on; 01/2005
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ABSTRACT: In this paper, we report on the infrared (IR) characterization of GaN films grown on Si substrate at various growth temperatures by low-pressure metalorganic chemical vapor deposition (LP-MOCVD) and electron cyclotron resonance plasma-assisted metal organic chemical vapor deposition (ECR-MOCVD). All the IR measurements were taken in the reflection mode and at room temperature by using Fourier transform infrared (FTIR) spectroscopy in s- and p-polarization. All results show that the structure type of the GaN deposited films is sensitive to the growth temperature and it can be correlated to the variation of the IR reststrahlen band. Our results also show that a good crystalline structure of GaN films can be grown at temperature higher than 600°C.
Semiconductor Electronics, 2002. Proceedings. ICSE 2002. IEEE International Conference on; 01/2003
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ABSTRACT: Ion implantation's high selectivity played a very important role in forming active device region and low resistance ohmic contact for bipolar and CMOS transistors. However the process of annealing for dopant activation and repair, problems related to anomalous transient enhanced diffusion (TED) negate the benefits of ion implantation. The irregular dopant diffusion makes the realization of sharp and shallow junction devices difficult. It is therefore very important to model the TED in relation to the implantation energy before any realistic design of the transistor can be made. In this work, both experimental result from special structures with different implantation energies and process simulator SILVACO SILVACO is studied and used to model TED.
Semiconductor Electronics, 2002. Proceedings. ICSE 2002. IEEE International Conference on; 01/2003
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ABSTRACT: A material system that appears to have a tremendous advantage and compatible with Si technology is the Si-SiGe system. One problem in npn SiGe HBT is boron out-diffusion from the base. Boron dopant that out-diffuses into the emitter and collector during SiGe growth and subsequent heat treatment results in the formation of parasitic energy barriers at the emitter/base and base/collector junctions. These barriers suppress the injection of electrons from the emitter to the collector which result in reduced collector current. In this work, a study on the non-linearity effects of the collector and base currents of the SiGe HBT is performed using a high performance process and device simulator SILVACO. The understanding of these effects is very important in the fabrication of high speed devices. The characteristics shows that the more out-diffusion of boron (B) at the emitter/base and base/collector junctions, the more non-ideal the currents. The underlying explanation for these trends will be discussed.
Semiconductor Electronics, 2002. Proceedings. ICSE 2002. IEEE International Conference on; 01/2003
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ABSTRACT: Bipolar transistors are well known for their high current driving capability and current gains, while CMOS transistors are dominant in the integrated circuit market because of their low power consumption and small size advantage. The combination of both types of transistor on the same chip provides a high performance circuit with a high packing density. In this work, 0.5 μm BiCMOS technology is fully utilized to realize silicon bipolar transistors with optimized performance. Preliminary electrical results are presented on bipolar transistors fabricated for the first time in Malaysia. Significant improvements in electrical device performance can be achieved by optimizing the emitter drive-in temperature and choice of annealing system
Semiconductor Electronics, 2000. Proceedings. ICSE 2000. IEEE International Conference on; 02/2000
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ABSTRACT: In this paper the analysis of multiple reflections in photonic crystal (PhC) multimode interference (MMI) couplers using eigen-mode expansion method is presented. The analysis is conducted on a hybrid PhC structure which consisted of 1-D PhC multimode waveguide sandwiched between 2-D PhC input/output waveguides. In PhC multimode waveguide, where the mechanism of wave confinement is not due to total internal reflection but due to photonic bandgap properties, the reflectivity at 2-D PhC facet wall would be very large for all the guided modes in the waveguide when ever the image formed due to MMI effect does not coincides with the output access waveguide.
Optics Communications 282(20):4063-4071. · 1.49 Impact Factor
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ABSTRACT: In this paper, we report for the first time on the use of IR reflectance spectroscopy to study the crystallinity of GaN films grown on Si substrate at various growth temperatures (i.e. from 50 °C to 1000 °C) by metalorganic chemical vapor deposition (MOCVD) and electron cyclotron resonance (ECR) plasma-assisted MOCVD. All results show that the structure type of the GaN deposited films is sensitive to the growth temperature. In addition, we also show that the crystalline structure of GaN films can be correlated to the variations of the IR reststrahlen band. Finally, we compared our results to the X-ray diffraction (XRD) results (i.e. taken from our earlier works); we found that both results are in good agreement. Hence, we suggest that IR reflectance spectroscopic can be used as an alternative technique to determine the crystallinity of the GaN deposited films as well as the IR optical properties.
Materials Chemistry and Physics.
