LEDs ♦ news digest


where GaN can now provide performance advantages not realisable in silicon LDMOS.”


“The higher operating voltage and higher efficiency possible with these new processes are key to rapid adoption,” adds Cengiz Balkas, vice president and general manager power and RF, Cree. “Switching to GaN for upcoming LTE/4G macro-cell base stations could save telecom operators over $2 billion annually in reduced energy costs. Fortunately, the telecom industry is beginning to recognize these potential savings. Cree is targeting to deliver more than 75 million watts of GaN transistors into telecom base stations this calendar year.”


At 40 volt operation, Cree’s G40V4 process exhibits up to 6 Watts/mm PSAT at 18 GHz. Typical device characteristics at 10 GHz are 65 percent power added efficiency (PAE) and 12 dB of small signal gain. At 50 V operation, the G50V3 process demonstrates up to 8 watts/mm PSAT at 6 GHz. Typical device performance at 3.5 GHz is 70 percent PAE with 12 dB of small signal gain. Both GaN processes are qualified for maximum operating channel temperature of 225ºC with a median time to failure of greater than 2E6 hours. In addition,


Cree is releasing MMIC design kits with proprietary scalable non-linear HEMT models suitable for operation with Agilent’s Advanced Design System (ADS) and AWR’s Microwave Office simulator platforms. The design kits also contain a full suite of passive components—resistors, capacitors, spiral inductors and substrate ground vias that can be used to simulate full MMIC performance and provide significantly reduced des


How to ‘heal’ plasma- damaged GaN with hydrogen radical treatment


Exposing plasma-damaged GaN to high doses of H radicals, restores the photoluminescence to almost the level of unetched GaN


Gallium nitride (GaN) is a highly promising material for a wide range of optical and high-power electronic devices, which can be fabricated by dry etching with plasmas.


However, the plasma-induced defects and surface residues that remain after such processes tend to degrade the optical and electrical properties of the devices.


Now, a team of Japanese researchers has developed and tested a new way to “heal” such defects.


The team exposed plasma-damaged GaN to hydrogen (H) radicals at room temperature. After testing various doses of H radicals, the researchers evaluated the optical properties of the GaN. The intensity of light emitted when electrons near the edge of the valence shell in GaN absorbed and then re-emitted photons drastically decreased after chlorine plasma-beam etching. After treatment with the higher-level doses of H radicals, however, the photoluminescence was restored to almost the level of unetched GaN.


The researchers say it is likely that the H radicals terminated the dangling bonds of gallium on the GaN surface, as well as desorbed the surface residues and that these two factors led to the recovered optical performance. A key characteristic of the new healing process is that it is performed in situ, immediately after the etching process. This is important because unwanted surface oxidation can easily occur on plasma-damaged GaN that is exposed to air.


Further details of this work have been published in the paper, “Photoluminescence recovery by in-situ exposure of plasma-damaged n-GaN to atomic hydrogen at room temperature,” by Shang Chen et al, AIP Advances, 2, 022149 (2012).


Cree reveals breakthrough GaN-based solid-state amplifier platform


The firm claims its breakthrough gallium nitride technology platform provides twice the efficiency of conventional gallium arsenide solutions


Cree is introducing a new 40 Volt, 0.25µm GaN- on-SiC HEMT process die product family to deliver revolutionary power and bandwidth capabilities through the Ku Band.


July 2012 www.compoundsemiconductor.net 155


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