Jingzhi Yin

Near-infrared light emitting diodes using PbSe quantum dots

Near infrared light emitting diodes (NIR LEDs) were fabricated employing blue GaN chips as the excitation source and PbSe quantum dots as the NIR emitting materials. Quantum dots with different emitting wavelengths were selected to fabricate three NIR LEDs corresponding to two typical applications of illumination and optical communication. The variation of emission peak and full width at half-maximum of the devices were investigated under different voltage bias, and the highest external quantum efficiency of 2.52% was achieved, which was comparable to those commercial InGaAsP LEDs and visible quantum dot electroluminescence LEDs.

Ultraviolet-enhanced light emitting diode employing individual ZnO microwire with SiO2 barrier layers

This paper details the fabrication of n-ZnO single microwire (SMW)-based high-purity ultraviolet light-emitting diodes (UV-LEDs) with an added SiO2 barrier layer on the p-Si substrate. However, the current-voltage (I-V) curve exhibited non-ideal rectifying characteristics. Under forward bias, both UV and visible emissions could be detected by electroluminescence (EL) measurement. When bias voltage reached 60u2009V at room temperature, a UV emission spike occurred at 390u2009nm originating from the n-ZnO SMW. Compared with the EL spectrum of the n-ZnO SMW/p-Si heterojunction device without the SiO2 barrier layer, we saw improved UV light extraction efficiency from the current-blocking effect of the SiO2 layer. The intense UV emission in the n-ZnO SMW/SiO2/p-Si heterojunction indicated that the SiO2 barrier layer can restrict the movement of electrons as expected and result in effective electron-hole recombination in ZnO SMW.

Tunable near-Infrared Luminescence of PbSe Quantum Dots for Multigas Analysis

Multigas sensing is highly demanded in the fields of environmental monitoring, industrial production, and coal mine security. Three near-infrared emission wavelengths from PbSe quantum dots (QDs) were used to analyze the concentration of three gases simultaneously through direct absorption spectroscopy, including acetylene (C2H2), methane (CH4), and ammonia (NH3). The corresponding lower detection limits for the three gases were 20, 100, and 20 ppm, respectively, with an accuracy of 2%. This study demonstrates that QDs with tunable emissions have great potential for simultaneous and uninterfered multiplex gas analysis and detection due to the advantages of the easy tunability of multiplex emitting wavelengths from QDs.

Ultraviolet-enhanced electroluminescence from individual ZnO microwire/p-Si light-emitting diode by reverse tunneling effect

In this study, heterojunction light-emitting diodes (LEDs) based on a ZnO single microwire (SMW) were fabricated on a p-Si substrate. Electroluminescence (EL) characteristics of this device operated at different biases were investigated. Ultraviolet (UV) and visible emission bands of the n-ZnO SMW/p-Si heterojunction device were observed under forward and reverse biases, respectively. When the reverse bias voltage reached 55 V, a sharp UV emission peak at ∼400 nm with a full width at half maximum of 20 nm dominated the EL spectra, and a satellite peak was located at ∼490 nm. The ratio of UV and defect emission intensity under the 55 V reverse bias was almost 28 times the ratio obtained under the 55 V forward bias. Our results indicated that the carrier transport process was affected by the tunneling effect, and this process could effectively suppress the defect emission and cause high UV emission efficiency in ZnO/Si-based ultraviolet LEDs. The emission mechanism of the heterojunction LED was discussed in terms of interface defect and energy band theory.

Study on the optical properties of β-Ga2O3 films grown by MOCVD

Abstractβ-Ga2O3 films were grown on c-plane sapphire substrates at different substrate temperatures by metal-organic chemical vapor deposition. The effects of substrate temperature on transparence, optical band gap and photoluminescence of the films were studied systematically. With increasing the substrate temperature, the films structure was changed from amorphous to single orientation β-Ga2O3. The β-Ga2O3 films exhibited excellent optical transparency in the ultraviolet and visible regions. The ultraviolet-blue photoluminescence was observed at room temperature. The temperature-dependent photoluminescence was also carried out and the relative intensity of the blue emission with respect to the ultraviolet emission decreased with increasing the measured temperature. The origin of luminescence was discussed.

Effect of annealing conditions on the structural, electrical and optical properties of Li-doped NiO thin films

Transparent conductive oxide (TCO) p-type Li-doped NiO thin films were deposited on the (0001) sapphire substrates by magnetron sputtering technique with a high purity NiO:Li2O ceramic target. We systematically investigated the structural, electrical and optical properties of NiO:Li thin films annealed in different conditions. We found that annealing in different conditions greatly affects the physical properties of NiO:Li thin films. Compared with the NiO:Li thin film annealed in oxygen, the hole concentration of NiO:Li thin film annealed in nitrogen at the same processing temperature is obviously lower. Annealed in oxygen at 500xa0°C, NiO:Li films show excellent crystal quality with single (111) orientation, high hole concentrations. When the annealing temperature increased, the transmittance of NiO:Li thin films become better for wavelength range from ultraviolet (UV) to visible with a significant absorption edge near 350xa0nm.

Growth of AlGaN-based multiple quantum wells on SiC substrates

Al0.2Ga0.8N/Al0.45Ga0.55N multiple quantum wells (MQWs) were grown on SiC substrates by metal–organic chemical vapor deposition. We studied the influence of well width and barrier width on the structural and optical properties of AlGaN MQWs in details. The MQWs structures prepared in this work all exhibited good periodicity and abrupt interfaces. When the barrier width was fixed, the thinner well was benefit to increase the integrated photoluminescence (PL) intensity of the MQWs and obtain a shorter ultraviolet wavelength. And the thicker barrier was also contributed to improve the optical properties while the well width remained the same. Compared with the effect of the well width, the emission wavelength of MQWs was less dependent on the barrier width. A 318-nm room-temperature PL emission was achieved when the well width and barrier width were 2.5 and 11xa0nm, respectively.