Excitation energy-dependent nature of Raman scattering spectrum in GaInNAs/GaAs quantum well structures

The excitation energy-dependent nature of Raman scattering spectrum, vibration, electronic or both, has been studied using different excitation sources on as-grown and annealed n- and p-type modulation-doped Ga(1 − x)In(x)N(y)As(1 − y)/GaAs quantum well structures. The samples were grown by molecular beam technique with different N concentrations (y = 0%, 0.9%, 1.2%, 1.7%) at the same In concentration of 32%. Micro-Raman measurements have been carried out using 532 and 758 nm lines of diode lasers, and the 1064 nm line of the Nd-YAG laser has been used for Fourier transform-Raman scattering measurements. Raman scattering measurements with different excitation sources have revealed that the excitation energy is the decisive mechanism on the nature of the Raman scattering spectrum. When the excitation energy is close to the electronic band gap energy of any constituent semiconductor materials in the sample, electronic transition dominates the spectrum, leading to a very broad peak. In the condition that the excitation energy is much higher than the band gap energy, only vibrational modes contribute to the Raman scattering spectrum of the samples. Line shapes of the Raman scattering spectrum with the 785 and 1064 nm lines of lasers have been observed to be very broad peaks, whose absolute peak energy values are in good agreement with the ones obtained from photoluminescence measurements. On the other hand, Raman scattering spectrum with the 532 nm line has exhibited only vibrational modes. As a complementary tool of Raman scattering measurements with the excitation source of 532 nm, which shows weak vibrational transitions, attenuated total reflectance infrared spectroscopy has been also carried out. The results exhibited that the nature of the Raman scattering spectrum is strongly excitation energy-dependent, and with suitable excitation energy, electronic and/or vibrational transitions can be investigated

An analysis of Hall mobility in as-grown and annealed n- and p-type modulation-doped GaInNAs/GaAs quantum wells

In this study, we investigate the effect of annealing and nitrogen amount on electronic transport properties in n- and p-type-doped Ga(0.68)In(0.32)N(y)As(1 − y)/GaAs quantum well (QW) structures with y = 0%, 0.9%, 1.2%, 1.7%. The samples are thermal annealed at 700°C for 60 and 600 s, and Hall effect measurements have been performed between 10 and 300 K. Drastic decrease is observed in the electron mobility of n-type N-containing samples due to the possible N-induced scattering mechanisms and increasing effect mass of the alloy. The temperature dependence of electron mobility has an almost temperature insensitive characteristic, whereas for p-type samples hole mobility is decreased drastically at T > 120 K. As N concentration is increased, the hole mobility also increased as a reason of decreasing lattice mismatch. Screening effect of N-related alloy scattering over phonon scattering in n-type samples may be the reason of the temperature-insensitive electron mobility. At low temperature regime, hole mobility is higher than electron mobility by a factor of 3 to 4. However, at high temperatures (T > 120 K), the mobility of p-type samples is restricted by the scattering of the optical phonons. Because the valance band discontinuity is smaller compared to the conduction band, thermionic transport of holes from QW to the barrier material, GaAs, also contributes to the mobility at high temperatures that results in a decrease in mobility. The hole mobility results of as-grown samples do not show a systematic behavior, while annealed samples do, depending on N concentration. Thermal annealing does not show a significant improvement of electron mobility

Dilute nitride resonant-cavity light emitting diode

Resonant cavity LEDs (RCLEDs) are a viable and low-cost alternative light source to lasers for optical communication systems in the 1.3 µm O-band. Most work in this area has been conducted on InP-based material, which is inherently costly, devices often require cooling and the refractive index contrast for constructing mirrors is low. Here, we demonstrate a high-performance GaAs-based RCLED using a dilute nitride GaInNAs active layer emitting in the 1.3 μm wavelength window. While previous 1.3 µm RCLEDs have used metallic mirrors on the back of the device, we exploit the high refractive index contrast of the GaAs/AlAs system to place Distributed Bragg mirrors on both sides of the active layer and achieve superior performance. The external quantum efficiency of the devices is 20% and the full width at half maximum of the emission spectrum is 5.2 nm at room temperature, into a narrow angular cone. The emission power from an 88 μm diameter aperture is 0.5 mW, which, together with the narrow spectral linewidth, makes the device suitable for deployment in a coarse Wavelength Division Multiplexing (WDM) communications system

Understanding the impact of heavy ions and tailoring the optical properties of large-area Monolayer WS2 using Focused Ion Beam

Focused ion beam (FIB) has been used as an effective tool for precise nanoscale fabrication. It has recently been employed to tailor defect engineering in functional nanomaterials such as two-dimensional transition metal dichalcogenides (TMDCs), providing desirable properties in TMDC-based optoelectronic devices. However, the damage caused by the FIB irradiation and milling process to these delicate atomically thin materials, especially in the extended area, has not yet been elaboratively characterised. Understanding the correlation between lateral ion beam effects and optical properties of 2D TMDCs is crucial in designing and fabricating high-performance optoelectronic devices. In this work, we investigate lateral damage in large-area monolayer WS2 caused by the gallium focused ion beam milling process. Three distinct zones away from the milling location are identified and characterised via steady-state photoluminescence (PL) and Raman spectroscopy. An unexpected bright ring-shaped emission around the milled location has been revealed by time-resolved PL spectroscopy with high spatial resolution. Our finding opens new avenues for tailoring the optical properties of TMDCs by charge and defect engineering via focused ion beam lithography. Furthermore, our study provides evidence that while some localised damage is inevitable, distant destruction can be eliminated by reducing the ion beam current. It paves the way for the use of FIB to create nanostructures in 2D TMDCs, as well as the design and realisation of optoelectrical devices on a wafer scale

Dağıtılmış Alt Bragg Dielektrik Yansıtıcılı Işık Yayan Diyot

Bu çalışmada alt Bragg yansıtıcısına sahip yakın kızılötesi bölgede ışıma yapan p-i-n diyotun tasarımı, fabrikasyon detayları ve elektro-optik özellikleri incelenmektedir.İncelenen ışık yayan aygıtın aktif ışıma bölgesi 20 adet GaInNAs/GaNAs (7 nm /13 nm) kuantum kuyusu sisteminden oluşmaktadır. Alt dielektrik aynası ise 15 adet GaAs/AlAs Bragg yansıtıcı çiftlerinin üst üste tabakasal olarak büyütülmesinden oluşmaktır. Aygıtın ışıma merkez dalgaboyu 1310 nm olup, spektral yarı genişliği 14.4 nm’dir. Işıma eşik akımı 20 nA olan aygıtın, 200 mA sürülen akım varlığında maksimum ışıma gücü 38 mW’dır. Bu çalışmada, yakın kızılötesi bölgede ışıma yapan aygıt üretilmesinin ve karakterize edilmesinin yanı sıra sadece alt Bragg yansıtıcı kullanılarak bile geleneksel ışık yayan diyotlara göre ışıma spektral genişliğinin ve ışıma profilinin iyileştirilebileceğini gösterilmiştir

ZnO nanoparticles-based vacuum pressure sensor

ZnO nanoparticles synthesized using the sol-gel technique with an average diameter of 11.5 nm are used to fabricate a vacuum pressure sensor in the range of 1 mbar to 10(+3) mbar (low vacuum limit). A drastic increase in the current of the drop-casted ZnO on glass with 30 mu m separated Au contacts defined by e-beam lithography is observed. The sensor reveals a linear relationship in current versus pressure in a logarithmic plot. In the range of 1 mbar to 10(+3) mbar, the sensor sensitivity is found be 110. Using the resistance-time plot of the vacuum pressure, the rise (response) and fall (recovery) times of the sensor are determined as 6.6 and 15.6 s, respectively. The power consumption of the sensor is 6.5 mu W. The operational parameters of the proposed sensor are found be much better than those of previously reported ZnO nanostructure-based sensors and, indeed, traditional ones. The sensing mechanism of the sensor is explained by the adsorption/desorption of OH(-)ions from the surface of the ZnO nanoparticles, leaving behind oxygen ions combined with oxygen vacancy states

Few-layer MoTe 2 -based Photodetector

2D MoTe2is highly attractive material due to its band gap of 1 eV which is compatible with near infrared optoelectronic applications such as LED, laser, photodetector. We present the fabrication details and performance of a metal- MoTe2-metal photodetector. We observed two main absorptions at 1 eV and 1.75 eV which are bandgap and high energy transition of few layer MoTe2. The dark current of photodetector is about 1 pA at applied bias of 3 V and the photocurrent of the devices is about 1under 6 mW excitation power. We concluded that few layer- MoTe2based MSM photodetector can be an alternative for its III-V group material-based counterparts

Determination of the acoustic phonon-hot carriers interaction in n- and p-type modulation-doped GaInNAs/GaAs quantum wells

© 2021 Elsevier B.V.We report on the power loss mechanisms of hot carries in as-grown and annealed n- and p-type modulation-doped GaAs/Ga0.68In0.32NyAs1-y (y = 0.009, and 0.012) quantum well structures considering acoustic phonon interactions via the deformation potential (non-polar) and piezoelectric (polar) scatterings. By analysis of the applied electric field dependent amplitude of the Shubnikov de Haas oscillations, it has been revealed that incorporation of N atom into Ga0.68In0.32As switches the dominant power loss mechanism from non-polar to polar mechanism. The piezoelectricity of n- and p-type Ga0.68In0.32NyAs1-y alloys is at least three times higher than N-free samples. A comparison between as-grown n- and p-type samples depicts that the p-type sample's piezoelectricity is higher than that of n-type samples. After thermal annealing, there is a slight decrement and increment in piezoelectric stress constant for n-type the sample with 0.9% and 1.2% N, respectively