Dresden 2003 – scientific programme
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HL: Halbleiterphysik
HL 4: GaN: Bauelemente
HL 4.3: Talk
Monday, March 24, 2003, 11:00–11:15, BEY/154
Photoionization Spectroscopy on AlGaN/GaN HEMTs grown on sapphire and on silicon — •Mike Wolter1, Peter Javorka1, Michel Marso1, Reinhard Carius2, Hans Lüth1, and Peter Kordoš1 — 1Institute of Thin Films and Interfaces - 1, Forschungszentrum Jülich, Germany — 2Institute of Photovoltaics, Forschungszentrum Jülich, Germany
The device performance of high electron mobility transistors (HEMTs) on AlGaN/GaN heterostructures is deteriorated by trapping processes. These processes are responsible for a reduction in the dc drain current (current collapse). The origin of the current collapse is assigned to deep level states in the layer system. Using photoionization spectroscopy we investigated these levels in HEMT structures grown by MOCVD on sapphire and on silicon. Whereas for HEMTs on sapphire we detected traps with excitation energies of about 3.2eV and 2.9eV, we found an additional trap at approximately 1.85eV for HEMTs on silicon. By varying the gate voltage we also found that a decrease of the gate bias leads to an increased photoionization cross section. This suggests that the concentration of electrons trapped in donor surface states has a strong influence on the current collapse process.