H. Abu Hassan

High sensitivity and fast response and recovery times in a ZnO nanorod array/p-Si self-powered ultraviolet detector

High quality, vertically aligned ZnO nanorods were grown on a silicon substrate, using microwave-assisted chemical bath deposition with poly (vinyl alcohol)-Zn(OH)2 nanocomposites as seed layer. The structure and surface morphology of the prepared ZnO nanorod arrays were characterized using X-ray diffraction and scanning electron microscopy. The optical properties were assessed using photoluminescence measurements; the results showed a high-intensity UV peak, and a lower intensity, broader visible peak. Upon exposure to 395 nm light at a zero-bias voltage, the UV detector showed a high sensitivity of 8000% and fast response and recovery times of 25 and 22 ms, respectively.

Experimental and theoretical studies of surface phonon polariton of AlN thin film

The surface phonon polariton (SPP) mode of aluminum nitride (AlN) thin film grown on sapphire substrate is investigated experimentally and theoretically. For the experimental study, p-polarized infrared attenuated total reflection measurements are performed. A strong absorption dip which corresponds to the SPP mode of AlN thin film is clearly observed at 839.0cm−1. For the theoretical study, the surface-polariton dispersion curve of the AlN thin film has been simulated. Finally, the experimental and theoretical values of the SPP mode are compared. The results revealed that the uncertainty between the theoretical and experimental SPP values is less than 2%.

Quaternary ultraviolet AlInGaN MQW laser diode performance using quaternary AlInGaN electron blocking layer

The effect of polarization-matched Al(0.25)In(0.08)Ga(0.67)N electron-blocking layer (EBL) on the optical performance of ultraviolet Al(0.08)In(0.08)Ga(0.84)N/Al(0.1)In(0.01)Ga(0.84)N multi-quantum well (MQW) laser diodes (LDs) was investigated. The polarization-matched Al(0.25)In(0.08)Ga(0.67)N electron blocking layer (EBL) was employed in an attempt to reduce the polarization effect inside the active region of the diodes. The device performance which is affected by piezoelectric was studied via drift-diffusion model for carrier transport, optical gain and losses using the simulation program of Integrated System Engineering Technical Computer Aided design (ISE TCAD). The optical performance of the LD using quaternary Al(0.25)In(0.08)Ga(0.67)N EBL was compared with the LD using ternary Al(0.3)Ga(0.7)N EBL where both materials have the same energy band gap of Eg = 3.53 eV. The self-consistent ISE-TCAD simulation program results showed that the polarization-matched quaternary Al(0.25)In(0.08)Ga(0.67)N EBL is beneficial as it confines the electrons inside the quantum well region better than ternary Al(0.3)Ga(0.7)N EBL. The results indicated that the use of Al(0.25)In(0.08)Ga(0.67)N EBL has lower threshold current and higher optical intensity than those for Al(0.3)Ga(0.7)N EBL. The effect of Al(0.25)In(0.08)Ga(0.67)N EBL thickness on the performance of LDs has also been studied. Results at room temperature indicated that lower threshold current, high slope efficiency, high output power, and high differential quantum efficiency DQE occurred when the thickness of Al(0.25)In(0.08)Ga(0.67)N EBL was 0.25 µm.

ZnO nanorod ultraviolet photodetector on porous silicon substrate

Vertically high-density ZnO nanorods were successfully synthesized on a porous silicon (PS) substrate by chemical bath deposition method. The structural and optical investigations revealed that the ZnO nanorods grown on the PS substrate had high structural and optical quality. The photoelectric properties of the fabricated photodetector were investigated with 325?nm UV light illumination under 1?V bias voltage. Based on the current?voltage curve, the responsivity of the ZnO nanorod photodetector was 1.738 A W?1?at 1?V bias voltage. Under a bias voltage of 1?V, the sensitivity of the ZnO nanorod device was 20. The response and recovery time of the ZnO nanorod photodetector under these conditions were 0.032 and 0.041?s, respectively.

Characteristics of photoconductive UV photodetector based on ZnO nanorods grown on polyethylene naphthalate substrate by chemical bath deposition method

Vertically aligned ZnO nanorods were synthesized on a polyethylene naphthalate (PEN) substrate using a chemical bath deposition method at a low temperature. The structural and optical investigations revealed the high quality of the fabricated ZnO nanorods on flexible substrate. A metal-semiconductor-metal UV photodetector based on ZnO nanorods was fabricated on the PEN substrate. The optoelectronic characteristics of fabricated UV photodetector were studied in the dark and under 325 nm UV light illumination at −3 V and 3 V bias voltages. The responsivity and photosensitivity of the ZnO nanorod UV photodetector were 2.856 A/W and 1175% at 3 V bias voltage, respectively. Moreover, the response and the recovery times measured during the turn-on and turnoff of UV illumination were 1.2 s and 1.8 s, respectively.

Surface phonon polariton mode of wurtzite structure AlxGa1−xN(0⩽x⩽1) thin films

Surface phonon polariton (SPP) mode of wurtzite structure AlxGa1−xN (0⩽x⩽1) thin films is investigated experimentally and theoretically. The influences of the alloy composition x on the position and the line width of SPP mode are reported. The results showed that the SPP absorption peak exhibits one-mode behavior and is subjected to broadening as x is increased. Reasonable agreement between the experimental and the theoretical results is also obtained. Finally, the composition dependence of the SPP mode with bowing parameter of −72.5cm−1 is determined.

Surface and interface phonon polaritons of wurtzite GaN thin film grown on 6H-SiC substrate

Surface and interface phonon polaritons of wurtzite GaN thin film grown on 6H-SiC substrate are investigated experimentally and theoretically. Two strong absorption peaks that correspond to the surface and interface phonon polaritons are clearly observed at 710 and 916 cm−1, respectively. This observation is in good agreement with the results simulated using an anisotropy model. Finally, the obtained surface phonon polariton (SPP) mode is compared with the reported result. It is revealed that the SPP mode in the wurtzite GaN thin film is shifted toward higher frequency as compared to that in the wurtzite bulk GaN.

Surface phonon polariton characteristic of honeycomb nanoporous GaN thin films

Nanoporous GaN thin films with honeycomb structure were fabricated via ultra-violet assisted electrochemical etching approach. Under different anodization voltages, two nanoporous samples with different porosity were fabricated. Porosity and surface phonon polariton (SPP) characteristics of the fabricated samples were investigated using polarized infrared attenuated total reflection technique. It was found that the porosity of nanoporous GaN has great influence on its SPP resonant frequency. It can modulate the resonance frequency towards lower value.

Porous Silicon as an Intermediate Buffer Layer for Zinc Oxide Nanorods

Zinc thin films were deposited onto porous silicon (PSi) substrates by dc sputtering using a Zn target. These films were then annealed under flowing (6 l/min) oxygen gas environment in the furnace at 600°C for 2 h. Porous silicon is used as an intermediate layer between silicon and ZnO films and it provides a large area composed of an array of voids. The PSi samples were prepared using photoelectrochemical method on n-type silicon wafer with (111) and (100) orientation. To prepare porous structures, the samples were dipped into a mixture of HF:ethanol (1:1) for 5 min with current densities of 50 mA/cm2, and subjected to external illumination with a 500 W UV lamp. The surface morphology and the nanorod structure of the ZnO films were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). We synthesized the ZnO nanorods with diameter of 80–100 nm without any catalysts or templates. The XRD pattern confirmed that the ZnO nanorods were of polycrystalline structure. The surface-related optical properties have been investigated by photoluminescence (PL) and Raman measurements at room temperature. Micro-Raman results showed that A1(LO) of hexagonal ZnO/Si(111) and ZnO/Si(100) have been observed at 522 cm–1 and 530 cm–1, respectively. PL spectra peaks are clearly visible at 366 cm–1 and 368 cm–1 for ZnO film grown on porous Si(111) and Si(100) substrates, respectively. The PL spectral peak position in ZnO nanorods on porous silicon is blue-shifted with respect to that in unstrained ZnO (381 nm).

Correlation of Raman and photoluminescence spectra of electrochemically prepared n-type porous GaAs

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.