The first European Gallium Nitride Workshop (EGW-1)

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The First European Gallium Nitride Workshop (EGW-I) by Mandeep Singh, Magus Research

The first European Gallium Nitride Workshop (EGW- 1) took place in Rigi, Switzerland, on June 2-4 1996. The aim of the workshop was to bring together leading researchers from academia and industry working on gallium nitride and related wide band-gap semiconductors. he two-day meeting consisted of four invited presentations and over sixtT short sevenminute contributions. At the end of each session a discussion period took place in which the speakers w e r e s u b j e c t e d to q u e s t i o n s f r o m the audience. The participants, numbering around 110, (see Fig. 1) had ample opportunity to interact with each other on issues brought up by the presentations. The impetus for the w o r k s h o p was provided by the e n o r m o u s worldwide interest in Gain driven mainly by the relatively recent realisation of blue LEDs, blue lasers and also solarblind photodetectors. The projected m a r k e t for these devices will be dominated by LED requirements for giant displays, desk-top flat-panel displays and traffic lights, for which high-output blue and g r e e n LEDs are essential. The biggest mass-market application for LEDs is envisioned to b e in t h e a r e a o f l i g h t i n g combining red, g r e e n and blue emitters for white light output. The realisation of a solid-state blue laser, w h i c h will have far-reaching implications for optical data storage and space and undersea communications, is the biggest p r e o c c u p a t i o n (overt or covert) of a large n u m b e r of the institutes and corporations rep r e s e n t e d at EGW-I. Although an electrically-pumped blue laser based on the InGaN/GaN multiple quantum well system was d e m o n s t r a t e d recently by Shuji Nakamura of Nichia Chemical, some w o r k still needs to be done to realise a low threshold

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and long lifetime laser diode suitable for commercial applications. In addition to the optoelectronics applications of the nitrides, high frequency and high t e m p e r a t u r e operation of devices are also under d e v e l o p m e n t but w e r e reported only briefly. Although GaN FETs continue to improve, it was the reluctant conclusion of the discussion at the end of the r u m p session that SiC devices will dominate in these areas. Another interesting area of c o m m e r cial interest r e p o r t e d was the possibility of p r o d u c i n g field emission i':T t %@~*~' ~

devices from GaN (similar to the diamond devices).

Technical Obstacles The main issues to arise from the meeting regarding the d e v e l o p m e n t of laser diodes and LEDs can be summarised as follows: • A solution must be found to the incorporation of a c c e p t o r dopants to obtain high p-type doping levels. • The microcracking in GaN films grown on sapphire substrates needs to be minimised.

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Dislocation densities m u s t be r e d u c e d for higher quantum efficiencies. • The p r o b l e m of establishing good Ohmic contacts is still a hurdle to overcome. • High thermal conductivity substrates are required for efficient heat dissipation. Point-like defects that act as recombination centres such as the ubiquitous yellow luminescence band in GaN do not appear to have a deleterious effect on device p e r f o r m a n c e and w e r e therefore relegated to the arena of fundamental research. •

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Applied Research and SVT Associates. The e q u i p m e n t market is likely to surge dramatically. In conclusion the overall impression of the w o r k s h o p was that it was an excellent forum for the delegates to mingle, although perhaps the sessions w e r e too formal and the time for discussions and debates was limited. On the other hand the r u m p session was well organised, informal and vibrant. We look forward to the n e x t w o r k s h o p in Valbonne, France, June 1997. An online version of this article can be found on the High T e m p e r a t u r e Electronics N e t w o r k WWW site at http://www.hiten.com

Devices

Dr Mandeep Singh, Magus Research, Rowlandson House, 289-293 Ballards Lane, London N12 8NP, UK Tel: + [44] (0) 181 4462505 Fax: +[44] (0) 181 4466483 E-mail: mandeep@ magus.co.uk

Disappointingly, few details w e r e provided on laser diode structures e x c e p t in passing. This is a result of the commercially-sensitive nature of this work, details of which the participants active in this area are reluctant to convey. However, some interesting devices w e r e reported: • M~,. Khan (APA Optics) discussed some AIGaN and GaN p-i-n structures, the prospects for GaN/SiC p-n junctions and d e m o n s t r a t e d the first a b r u p t junction n - G a N / p G a N diode. • AIGaN/GaN HEMTs with 0.25 micron gate lengths yielding ft = 22GHz and fm = 77GHz w e r e r e p o r t e d by L. Eastman (Cornell University). • Heterojunction diodes with a n-GaN/p-SiC structure fabricated by Cree Research EED w e r e r e p o r t e d by A.E. Nikolaev and coworkers w h o formed mesa structures by reactive ion etching. These structures showed good rectifying characteristics. • J.I. Pankove (Astralux Inc.) r e p o r t e d a high power, high t e m p e r a t u r e heterojunction bipolar transistor with a nGaN/p-SiC/n-SiC structure (where n-GaN is the emitter) capable of operating adequately at 520°C.

Opposing Camps The nitride c o m m u n i t y is divided into opposing camps on a n u m b e r of key issues. Crystal growers are in constant discussions about the relative merits of the MOVPE and MBE growth methods. Then, in terms of bulk substrates, there is one school that favours substrates such as sapphire rather than SiC on the grounds of cost and the fact that adequate p e r f o r m a n c e devices can be fabricated on these substrates. H o w e v e r the SiC school led by Cree (which of course has an in-house source of substrate supply) counter by citing the superior thermal conductivity of SiC and the fast improving quality of the SiC/GaN heterojunction interface. The two variants are likely to co-exist and the choice of substrate will be governed by the device requirements.

Equipment Market to Surge It is clear that the nitrides technologies show sufficient promise to warrant large scale production (initially of high-brightness blue and green LEDs). Nichia Chemical recently a n n o u n c e d that it has put in place capacity for manufacturing 5 million units per month. For this reason the v a c u u m e q u i p m e n t m a n u f a c t u r e r s and g r o w t h reactor manufacturers w e r e out in force. The companies r e p r e s e n t e d included AIXTRON, EMCORE, EPI, Oxford

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