Aug 9, 2019

Transfer-free fabrication of a graphene transparent electrode on a GaN-based light-emitting diode using the direct precipitation method

In order to advance the mass production of graphene devices, it is beneficial to avoid the difficulty graphene transfer process. Direct precipitation of graphene using a tungsten capping layer is convenient for this purpose, and is quite simple and compatible with conventional semiconductor fabrication processes. In this study, multilayer graphene was directly precipitated on a wafer of GaN-based blue LEDs to form a transparent electrode. The fabricated LED exhibited superior I–V characteristics and emitted blue luminescence around the probe of the electrode.


Source:IOPscience

For more information, please visit our website: www.semiconductorwafers.net,

Aug 1, 2019

Liquid Phase Epitaxy of Si-Doped GaAs for Efficient Light Emitting Diodes

The Si doped expitaxial growth of GaAs by the rolling boat method and the fabrication of efficient light emitting diodes are represented. During the growth on GaAs (111) B substrate, highly efficient diodes are obtained when the amount of Si added to 5 g of Ga is 6 mg and the Ga solution is baked at 910°C for 1 hour prior to the growth. The highest power efficiency is 9.7 % for an uncoated flat diode. The epitaxial wafer uniformity depends upon whether growth spirals occur or not. The efficiency of light emitting diodes fabricated from a wafer with growth spirals varies from ~2 to ~9 %. On the other hand, that with no spirals varies from ~6 to ~9 %. The occurrence of the growth spirals can be controlled by changing the rolling start time.



Source:IOPscience

For more information, please visit our website: www.semiconductorwafers.net,

Jul 23, 2019

High-Bright InGaN Multiple-Quantum-Well Blue Light-Emitting Diodes on Si (111) Using AlN/GaN Multilayers with a Thin AlN/AlGaN Buffer Layer

InGaN multiple-quantum-well (MQW) blue light-emitting diodes (LEDs) on Si (111) substrate were grown by metalorganic chemical vapor deposition. Crack-free films on 2-inch wafer were obtained using AlN/GaN multilayers with a thin AlN/AlGaN buffer layer. High-resolution X-ray diffraction (HRXRD) reveals the LED on Si is of high crystalline quality. Dislocation density of MQW active layer was investigated by cathodoluminescence (CL) at room temperature. The operating voltages of 3.7 V and 4.2 V and the output powers of 34.8 µW and 34.5 µW at 20 mA were obtained for the lateral and the vertical conduction, respectively. The forward series resistances are 33 Ω and 42 Ω for the lateral and the vertical conduction, respectively. The EL peaks at 453 nm with a full width at half maximum (FWHM) of 22 nm at 20 mA current. These characteristics are comparable to those of LED on sapphire. Especially, the LED on Si shows a high saturation operating current due to the good thermal conductivity of Si substrate.



Source:IOPscience

For more information, please visit our website: www.semiconductorwafers.net,

Jul 17, 2019

Exfoliation of AlN film using two-dimensional multilayer hexagonal BN for deep-ultraviolet light-emitting diodes

Crack-free crystalline AlN film was synthesized on two-dimensional multilayer hexagonal BN (h-BN) by metal organic vapor phase epitaxy (MOVPE). The multilayer h-BN was directly grown on sapphire substrates in wafer scale by MOVPE, with a thickness of 2.9 nm. The AlN film grown on the h-BN/sapphire presented a smooth surface. We further realized the exfoliation of AlN film utilizing the weak bonds within h-BN layers. Moreover, the AlGaN-based deep-ultraviolet light-emitting diodes grown on the AlN/h-BN/sapphire template exhibited obvious emissions at 281 nm. It is promising that the multilayer h-BN will pave the way to obtain transferable high-efficiency devices with wafer scale.



Source:IOPscience

For more information, please visit our website: www.semiconductorwafers.net,

Jul 9, 2019

Highly Uniform Electroluminescence from 150 and 200 mm GaN-on-Si-Based Blue Light-Emitting Diode Wafers

We report on the on-wafer device characteristics of 150 and 200 mm GaN-on-Si-based blue LED wafers grown by metalorganic chemical vapor deposition on Si(111) substrates with electroluminescence at 447 nm. Excellent uniformity was achieved with standard deviations of 3.9% for the electroluminescence intensity, 0.6–0.8% for the peak wavelength and 1.3% for the forward voltage. The high uniformity confirms the viability of the GaN-on-Si technology on large-diameter substrates for next-generation LED manufacturing. The reverse bias current leakage mechanism is also investigated to provide an insight into improving device reliability.



Source:IOPscience

For more information, please visit our website: www.semiconductorwafers.net,

Jun 20, 2019

Stress Engineering by Controlling Sapphire Substrate Thickness in 520 nm GaN-Based Light-Emitting Diodes

Controlling the compressive stress in 520 nm GaN-based light-emitting diodes (LEDs) prepared on sapphire substrates with different thicknesses was investigated. As the sapphire substrate thickness is reduced, the compressive stress in the GaN layer is released, resulting in wafer bowing. The wafer bowing-induced mechanical stress alters the piezoelectric fields, which in turn reduces the quantum-confined Stark effect in the InGaN/GaN active region of the LED. Thus, the electroluminescence spectral peak wavelength was blue-shifted, and the internal quantum efficiency was improved by about 11% at an injection current of 20 mA. The LED with an 80-µm-thick sapphire substrate exhibited the highest light output power of 11.5 mW.



Source:IOPscience

For more information, please visit our website: www.semiconductorwafers.net,

Jun 14, 2019

Efficient textured colour conversion layer of a down-converted white organic light-emitting diode by transfer imprinting

In this paper, we demonstrated an efficient textured colour conversion layer (CCL) of a down-converted white organic light-emitting diode (WOLED), which was fabricated by a very simple transfer imprinting method based on silicon wafer. The textured CCL not only helped to extract wave-guided light in the device, but also had an outstanding performance in enhancing the colour conversion rate, which was 1.75 times greater than that of flat CCL. Compared to flat CCL, the lower-doped textured CCL produced better white emission and higher efficiency simultaneously. Moreover, the WOLED with textured CCL also exhibited good colour stability at various voltages.



Source:IOPscience

For more information, please visit our website: www.semiconductorwafers.net,