Apr 18, 2019

200-mm GaN-on-Si Based Blue Light-Emitting Diode Wafer with High Emission Uniformity

We investigated the emission wavelength uniformity of 200-mm GaN-on-Si based blue light-emitting diode (LED) wafer grown by metalorganic vapor phase epitaxy (MOVPE). The larger the Si substrate diameter becomes, the more difficult to obtain uniform distribution of the emission wavelength because of the larger bow during growth, resulting in larger on-wafer inhomogeneity in growth temperature. Owing to the GaN-on-Si buffer strain management, optimized gas flow condition, and precise control of temperature balance in a reactor, we have achieved high thickness and crystal quality uniformity over the 200-mm GaN-on-Si based blue LED wafer. As a result, excellent blue photoluminescence emission wavelength uniformity from the InGaN-multi-quantum wells can be demonstrated on a 200-mm wafer with a standard deviation of 2.53 nm (0.57%). Less wavelengths binning with these highly uniform emission over the 200-mm wafer show the capability of sustainable cost reduction in LED fabrication based on GaN-on-Si technology.


Source:IOPscience

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

Apr 9, 2019

The influence of undoped GaN surface flatness on the properties of the blue light-emitting diode wafer

We have studied the properties of blue-LED wafers grown on GaN with similar dislocation density and different surface flatness. Results indicate that the smooth surface morphology of the undoped GaN layer leads to better layer periodicity in multiple quantum well (MQW) and smooth surface morphology of LED wafers. The surface flatness of the undoped GaN layer has little effect on the forward voltage and output power of the LED. However, the reverse leakage current and the lifetime of the LED wafer grown on the flatter GaN layer improved evidently. On the other hand, wafers grown on the GaN layer with worse surface flatness show better electrostatic discharge (ESD) characteristics.



Source:IOPscience

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

Apr 3, 2019

Effect of surface treatment of GaN based light emitting diode wafers on the leakage current of light emitting diode devices

To form low-resistance Ohmic contact to p-type GaN, InGaN/GaN multiple quantum well light emitting diode wafers are treated with boiled aqua regia prior to Ni/Au (5 nm/5 nm) film deposition. The surface morphology of wafers and the current–voltage characteristics of fabricated light emitting diode devices are investigated. It is shown that surface treatment with boiled aqua regia could effectively remove oxide from the surface of the p-GaN layer, and reveal defect-pits whose density is almost the same as the screw dislocation density estimated by x-ray rocking curve measurement. It suggests that the metal atoms of the Ni/Au transparent electrode of light emitting diode devices may diffuse into the p-GaN layer along threading dislocation lines and form additional leakage current channels. Therefore, the surface treatment time with boiled aqua regia should not be too long so as to avoid the increase of threading dislocation-induced leakage current and the degradation of electrical properties of light emitting diodes.


Source:IOPscience

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

Mar 26, 2019

Monolithic integration of Si-MOSFET and GaN-LED using Si/SiO2/GaN-LED wafer

In this report, we present a monolithic integration method for a Si-MOSFET and a GaN-LED onto a Si/SiO2/GaN-LED wafer as an elemental technology for monolithic optoelectronic integrated circuits. To enable a Si-MOSFET device process, we investigated the thermal tolerance of a thin top-Si and GaN-LED layer on a Si/SiO2/GaN-LED wafer. The high thermal tolerance of the Si/SiO2/GaN-LED structure allowed for the monolithic integration of a Si n-MOSFET and a GaN-µLED without degrading the performance of either device. A GaN-µLED driver circuit was fabricated using a Si n-MOSFET and a µLED of 30 × 30 µm2, with the modulation bandwidth of the circuit estimated to be over 10 MHz.


Source:IOPscience

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

Mar 18, 2019

A Flip-Chip AlGaInP LED with GaN/Sapphire Transparent Substrate Fabricated by Direct Wafer Bonding

A red-light AlGaInP light emitting diode (LED) is fabricated by using direct wafer bonding technology. Taking N-GaN wafer as the transparent substrate, the red-light LED is flip-chiped onto a structured silicon submount. Electronic luminance (EL) test reveals that the luminance flux is 130% higher than that of the conventional LED made from the same LED wafer. Current–voltage (I–V) measurement indicates that the bonding processes do not impact the electrical property of AlGaInP LED in the small voltage region (V<1.5 V). In the large voltage region (V>1.5 V), the I–V characteristic exhibits space-charge-limited currents characteristic due to the p-GaAs/n-GaN bonding interface.



Source:IOPscience

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

Mar 12, 2019

Milliwatt power UV-A LEDs developed by using n-AlGaN superlattice buffer layers grown on AlN templates

Ultraviolet (UV)-A light-emitting diode (LED) light sources are strongly demanded for both medical and photochemical applications. In our previous report, we investigated the conventional n-AlGaN buffer layer (BL)-based UV-A LED devices and a very low output power was achieved. In this work, we aim for the suppression of vertically propagating threading dislocation densities (TDDs) in the n-AlGaN BL including the current spreading layer (CSL) by introducing Si-doped n-Al0.37Ga0.63N/n-Al0.27Ga0.73N superlattices (SLs) between the AlN template and n-AlGaN BL for the demonstration of 341 nm UV-A LEDs. When the conventional n-AlGaN BLs were replaced with n-AlGaN SL-based BLs (with a suitable number of periods up to ~70) in the UV-A multi-quantum wells, then the full width at half maximum of the x-ray rocking curves in the n-AlGaN CSL for the (0 0 0 2) and (10–12) planes, respectively, were reduced to 346 and 431 arcsec and the total TDDs were suppressed to approximately ~1  ×  109 cm−2. Finally, when the conventional Ni (20 nm)/Au (150 nm) p-electrodes were replaced with new Ni (1 nm)/Mg (200 nm) p-electrodes in the n-AlGaN SL-based UV-A LEDs, the maximum output power was improved from 2.1 to 2.5 mW.


Source:IOPscience

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

Mar 5, 2019

Fabrication technology for high light-extraction ultraviolet thin-film flip-chip (UV TFFC) LEDs grown on SiC

The light output of deep ultraviolet (UV-C) AlGaN light-emitting diodes (LEDs) is limited due to their poor light extraction efficiency (LEE). To improve the LEE of AlGaN LEDs, we developed a fabrication technology to process AlGaN LEDs grown on SiC into thin-film flip-chip LEDs (TFFC LEDs) with high LEE. This process transfers the AlGaN LED epi onto a new substrate by wafer-to-wafer bonding, and by removing the absorbing SiC substrate with a highly selective SF6 plasma etch that stops at the AlN buffer layer. We optimized the inductively coupled plasma SF6 etch parameters to develop a substrate-removal process with high reliability and precise epitaxial control, without creating micromasking defects or degrading the health of the plasma etching system. The SiC etch rate by SF6 plasma was ~46 μm hr–1 at a high RF bias (400 W), and ~7 μm hr–1 at a low RF bias (49 W) with very high etch selectivity between SiC and AlN. The high SF6 etch selectivity between SiC and AlN was essential for removing the SiC substrate and exposing a pristine, smooth AlN surface. We demonstrated the epi-transfer process by fabricating high light extraction TFFC LEDs from AlGaN LEDs grown on SiC. To further enhance the light extraction, the exposed N-face AlN was anisotropically etched in dilute KOH. The LEE of the AlGaN LED improved by ~3× after KOH roughening at room temperature. This AlGaN TFFC LED process establishes a viable path to high external quantum efficiency and power conversion efficiency UV-C LEDs.



Source:IOPscience

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