Regensburg 2004 – wissenschaftliches Programm
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HL: Halbleiterphysik
HL 16: GaN: Bauelemente
HL 16.8: Vortrag
Dienstag, 9. März 2004, 12:00–12:15, H13
Optimized Specific Contact Resistance of p-GaN — •Jens Dennemarck1, Tim Böttcher1, Detlef Hommel1 und Anna Piotrowska2 — 1Institute of Solid State Physics, University of Bremen, D-28359 Bremen — 2Institute of Electron Technology, Al. Lotnikow 32/46, 02-668 Warsaw, Poland
Nowadays GaN-based high performance devices are available, which needs high current densities during operation. For example, a GaN-based laser diode needs a current density in the range of some 1 kA/cm2. To operate devices reliable with such high driving conditions, ohmic contacts with quite low specific contact resistances are necessary.
In the case of p-type GaN a metal with a large work function is necessary. Then the difference between vacuum and Fermi level is large, that holes can get into the metal without a barrier.
Two approaches were performed to reduce the specific contact resistance: first a highly doped cap layer with a thickness of 15nm was added. This should increase the number of acceptor levels with the effect of a decreased barrier height. The second approach was a InGaN subcontact layer about 20 nm. In respect of the induced strain the thickness of the barrier decreased. To measure the specific contact resistance, the transfer length method (TLM) was used. The problems of this measurement are current spreading and current crowding. The cTLM method (circular TLM) was considered to be the better method.
A number of metallization with different work functions were applied. The best results were achieved by Pd/Au contacts with a specific contact resistance of 1-2*10-5 A/cm2.