Yushamdan Yusof

InN PHOTOCONDUCTORS ON DIFFERENT ORIENTATIONS OF Si SUBSTRATES

We have fabricated photoconductors of indium nitride (InN) grown by radio frequency (RF) sputtering. The InN thin films were deposited on Si(100), Si(110) and Si(111) substrates at room temperature. The Ag/Al contact has been deposited by thermal evaporation in vacuum (10-5Torr) and then annealed under the flowing of the nitrogen gas environment in order to relieve stress and also induce any favorable reactions between metals and the semiconductor. Current–voltage (I–V) measurements after heat treatment at 400°C were carried out for samples in dark and illumination conditions. It was found that Ag/Al formed a good ohmic contact on top of InN. In addition, the characteristics of the contacts were significantly affected by the orientation of substrates.

Fabrication Gallium Nitride (GaN) Nanowires by Thermal Chemical Vapor Deposition (TCVD) Technique

In this paper, low-dimensional gallium nitride (GaN) nanowires have been successfully grown on silicon substrate through thermal chemical vapor deposition (TCVD); no metal catalyst was used to assist growth of nanostructure. A high purity of gallium nitride powder was used as a starting material, evaporated at 1150 OC for 2 hour and then annealing at temperature 1000 OC under stable flow of ammonia (NH3) gas in horizontal quartz tube. The morphological investigation and crystalline and orientations growth of GaN nanostructure were carried out by employing scanning electron microscopy (SEM), high resolution X-ray diffractmeter (HRXRD). A room temperature micro-Raman spectrum were employed to study the optical properties and crystalline defects. XRD shows the diffraction peaks located at 2θ= 32.43, 34.57, 36.89, 48.05, 57.83, 63.62, 69.02, and 70.470 corresponding to the (100 ), (002), (101), (102), (110) , (103),(112 ) and (201) plane diffraction of GaN structure. These results revealed that the diffraction peaks can be attributed to hexagonal GaN phase with lattice constant of a = 3.190 A° and c = 5.1890 A°. Here we report on the growth of GaN nanowires on Si (111) substrate by CVD . This technique is much simpler and cheaper than such techniques as MBE, MOCVD and HVPE.

Catalyst‐free growth and characterization of ZnO nanoscrewdrivers prepared by thermal evaporation

Purpose – The purpose of this paper is to propose a simple physical evaporation route in which catalyst‐free zinc oxide (ZnO) nanoscrewdrivers were deposited on silicon (Si) (111) substrates.Design/methodology/approach – Prior to the deposition, the Si (111) wafer was cut into pieces of 2×2 cm2. Then, the wafers were dipped for 1 min into mixture buffered oxide etchant to remove native oxide. Then, the samples were rinsed in an ultrasonic bath cleaned with boiling acetone, ethanol, and de‐ionized (DI) water for 10 min. Lastly, the wafers were rinsed in 25 ml DI water in stirred and then were blown dry with nitrogen. In this technique, the starting material is high‐purity metallic zinc (Zn) powder (99.99 per cent pure). Following, the Zn films were then annealed under air environment in the furnace at 500°C for 1 h deprived of any catalysts.Findings – These ZnO samples were studied by scanning electron microscopy, high‐resolution X‐ray diffraction (HR‐XRD), and photoluminescence (PL) spectroscopy. Atomic f...

Structural characterization of AlN and AlGaN layers grown on GaN/AlN/Si 111 by plasma-assisted MBE

Aluminum nitride (AlN) and high aluminum (Al) content aluminum gallium nitride (AlGaN) thin films were successfully grown on gallium nitride (GaN) layer by plasma-assisted molecular beam epitaxy (PA-MBE) system. The films were deposited on Si 111 substrate. A systematic study and optimization of the growth conditions was performed in order to grow AlN and AlGaN layers on GaN films. Epitaxial growth of GaN has been demonstrated to be feasible for substrate temperature (800°C and 850°C) which depends on a Ga/nitrogen flux ratio. The absence of cubic phase GaN buffer layer for both samples has shown that this layer possessed hexagonal structure. The AlN sample has a good optical quality as measured by the photoluminescence (PL) system.

The Fabrication of Ag Islands on AlN/GaN/AlN/Si(111) by Using Thermal Evaporator and Thermal Annealing Methods

In this paper, we studied growth of AlN/GaN/AlN on Si (111) by using plasma assisted molecular beam epitaxy (PA-MBE) system. The structural and optical characteristics of the sample have been investigated by using high resolution X-ray diffraction (HR-XRD), Raman spectroscopy and photoluminescence (PL). PL spectrum of the sample has shown sharp and intense band edge emission of GaN with the absence of yellow emission band, indicating good crystal quality of the sample. The silver (Ag) metal contact was then deposited on the sample followed by thermal treatment at 500°C and 700°C, respectively. Treated sample at 700°C showed good spherical Ag islands on sample compared to the treated sample at 500°C. The effect of Ag islands on the electrical characteristics of sample was also examined by using I-V measurement. The results showed that the treated sample at 700°C has decreased the photo-current of Schottky diode.

The effect of ecthing duration on structural properties of porous Si fabricated by a new two-steps alternating current photo-assisted electrochemical etching (ACPEC) technique for MSM photodetector

This project presents a new method to fabricate porous Si using two-step Alternating Current Photo-Assisted Electrochemical Etching (ACPEC) technique. The n-type Si (111) was initially etched for a short time to form high density of etch pits and subsequently the sample was anodized in HF solution by using alternating current photo-assisted electrochemical etching (ACPEC) technique. The study aims to investigate the effect of different etching duration on the properties of porous Si. This new method of porous Si fabrication produced higher density, porosity and more uniform distribution of triangular-like pores compared to the sample etched without the initial etching. We observed that the pore size, porosity and average surface roughness were increased with etching duration. Amongst the samples, the 10 minutes of etched sample showed the maximum pore diameter and porosity. Subsequently, metal-semiconductor-metal (MSM) photodetector have been fabricated by depositing Al metal contacts on the non-porous an...

Investigation on the structural characterization of pulsed p-type porous silicon

P-type Porous silicon (PS) was sucessfully formed by using an electrochemical pulse etching (PC) and conventional direct current (DC) etching techniques. The PS was etched in the Hydrofluoric (HF) based solution at a current density of J = 10 mA/cm2 for 30 minutes from a crystalline silicon wafer with (100) orientation. For the PC process, the current was supplied through a pulse generator with 14 ms cycle time (T) with 10 ms on time (Ton) and pause time (Toff) of 4 ms respectively. FESEM, EDX, AFM, and XRD have been used to characterize the morphological properties of the PS. FESEM images showed that pulse PS (PPC) sample produces more uniform circular structures with estimated average pore sizes of 42.14 nm compared to DC porous (PDC) sample with estimated average size of 16.37nm respectively. The EDX spectrum for both samples showed higher Si content with minimal presence of oxide.

The study of GaN pn-junction grown on Si substrate by MBE with Ni/Ag as ohmic contact

The gallium nitride (GaN) pn-junctions was grown on silicon (111) substrate by plasma assisted molecular beam epitaxy (PA-MBE) on top of a AlN buffer in order to reduce the strain of the alloy. For GaN pn-junction layers, silicon and magnesium were used as n and p dopants, respectively. The SEM images show a high quality hetero-interface without cracking by optimizing the growth conditions. The full width at half-maximum (FWHM) of the GaN pn-junctions deposited on silicon as determined by X-ray diffraction (XRD) symmetric rocking curve (RC) ω/2θ scans of (0002) plane at room temperature is 0.34°. Raman results show the maximum intensity at 523.63 cm-1 which is attributed to crystalline silicon. All the allowed Raman optical phonon modes of GaN, i.e. the E2 (low), E1 (high) and A1 (LO) are clearly presented, which are located at 147.76 cm-1, 571.65 cm-1 and 737.9 cm-1, respectively. The presence of E1 (high) has led to the evidence of hexagonal-phase character for this GaN pn-junction layer. The non-existence of yellow band emission in PL result confirmed that the thin film is of good optical quality. The GaN pn-junction diode shows a rectifying behavior of current under forward bias.

The study of undoped ZnO/p-Si (111) thin films prepared by R.F. magnetron sputtering

We report on the investigation of zinc oxide (ZnO) thin films grown on p-type silicon (111) substrate by radio frequency (RF) magnetron sputtering tool. The structural and optical characteristics of the sample have been investigated by using scanning electron microscope (SEM), atomic force microscope (AFM), high resolution X-ray diffraction (HR-XRD), Raman spectroscopy, photoluminescence (PL) and Fourier transform infra-red (FTIR), respectively. The FTIR measurement reveals that ZnO retains its wurtzite structure due to the presence of vibrations in the Zn-O bonds. XRD analysis shows that there exists a slight impurity occurring in the sample with the presence of Al2O3 and the high and sharp peak of ZnO shows the good quality of crystallinity of ZnO. Raman spectroscopy measurements reveal that the ZnO film is a single crystal and has wurtzite structure and the presence of impurities such as oxygen deficiencies and interstitial defects. The PL spectra clearly prove that the Zn has high crystal quality due to the very high and sharp peak at wavelength of 390 nm. The deep level emissions also show that there is an oxygen defects in the ZnO film. The deposition of ZnO film onto Si substrate through RF sputtering results in the ZnO film having high quality crystal structure with the presence some impurities and defects.

Compositional and Structural Characterization of Heterostructure InGaN-Based Light-Emitting Diode by High Resolution X-Ray Diffraction

This paper focuses on the compositional and structural characterization of InGaN-based light-emitting diode (LED) using high resolution x-ray diffraction (HRXRD) system. The LED was epitaxially grown on Si (111) substrate that comprises of In0.11Ga0.89N multi-quantum-well (MQW) active layer. Phase analysis 2θ-scan proved the composition of GaN (0002) and (0004) at 34.63o and 72.98o, respectively. Rocking curve φ-scan showed six significant peaks of the hexagonal GaN structures with consistent angular gaps of ~60o. From x-ray rocking curve (XRC) ω-scan, screw and mix dislocation density is found as 2.85 × 109 cm-2, while pure edge dislocation density is found as 2.23 × 1011 cm-2.