news digest ♦ LEDs
dominate demand over the forecast period. Further, it is expected to exhibit the fastest growth from 2014 to 2020, due to government initiatives favoring COB LED adoption and a large number of market participants.
Key firms operating in the market include Philips LumiLEDs Lighting Company, Cree Inc, Samsung Electronics Co Ltd, Citizen Electronics Co Ltd, Osram Opto Semiconductors GmbH, Everlight Electronics Co Ltd., Seoul Semiconductor Co Ltd, Nichia Corp, Lumens Co Ltd, and LG Innotek Co Ltd.
The market is consolidated in nature, and the development of efficient and cost-effective products is expected to serve as a key growth strategy over the forecast period.
Hong Kong team integrates on-chip light source with III- nitride electronics
Approach holds promise for synchronous RF/optical comms and more...
Integrating III-nitride-based light-emitting and electronic control devices would help make more compact optoelectronics systems such as on- chip lighting control, synchronous RF/optical communications, and opto-couplers for power conversion. But attempts to grow LED and HEMT structures on the same substrate have been hampered by the incompatibility of their optimised growth temperatures and by the complexity of integrated devices with different active layers.
Now a team from Hong Kong University of Science and Technology has reported producing GaN band-edge ultraviolet emission at 3.4eV at room temperature, at a small forward bias larger than -2V, from a simple metal-AlGaN/GaN Schottky diode. Their findings were published in Applied Physics Letters 105 (2014).
Schottky-drain electrode in an AlGaN/GaN HEMT
The researchers’ goal was to produce electroluminescence (EL) at room temperature from metal-AlGaN/GaN Schottky diodes on a conventional doping-free III-nitride heterostructure suitable for HEMTs. (EL was first discovered in a metal-SiC structure in 1907. EL emissions from Schottky diodes on Si, II-VI, and III-V semiconductor have also been reported by research groups over the last 30 years).
By employing a semi-transparent Schottky-drain electrode in an AlGaN/GaN HEMT, the team succeeded in building a UV high electron mobility light-emitting transistor (HEM-LET) in a relatively straightforward manner. Figure a) below presents the schematic device structure of the device demonstrated in this work.
The team used an AlGaN/GaN heterostructure consisting of a 21nm Al 0.25Ga 0.75 N barrier and 3.8µm GaN buffer, grown by MOCVD on a 4inch p-type S (111) substrate. The heterostructure contained a 2DEG channel of density 1013 mobility 2080cm2
/cm-2 /V-1 s-1 at room temperature.
They defined the ohmic contacts using photolithography and formed them with Ti/Al/Ni/ Au metallisation annealed at 850degC for 30s in N 2 ambience. Remote plasma pretreatment in an atomic-layer-deposition (ALD) machine was used to remove the residual native oxide and nitridise the surface. The passivation and surface protection layer was an AlN/SiN x (4/50nm) stack.
After the Schottky area was defined with photolithography, the SiN x was dry etched by a low-power plasma process and the AlN thin film removed by dilute alkaline solution. Then the semitransparent Schottky metal Ni/Au (5/6 nm)
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