Polarization dependent analysis of AlGaN/GaN HEMT for high power applications Parvesh Gangwani a , Sujata Pandey b , Subhasis Haldar c , Mridula Gupta a , R.S. Gupta a, * a Semiconductor Devices Research Laboratory, Department of Electronic Science, University of Delhi South Campus, New Delhi 110 021, India b Amity School of Engineering and Technology, New Delhi, India c Motilal Nehru College, University of Delhi, Benito Juarez Road, New Delhi 110 021, India Received 18 May 2006; received in revised form 28 October 2006; accepted 3 November 2006 Available online 17 January 2007 The review of this paper was arranged by Prof. E. Calleja Abstract Polarization dependent analysis for AlGaN/GaN HEMT has been done. The capacitance–voltage characteristics of lattice mis- matched AlGaN/GaN modulation doped field effect transistor are obtained using charge controlled analysis for its microwave perfor- mance. The model includes the spontaneous and piezoelectric polarization effects and device transconductance and cutoff frequency are calculated. The results show excellent agreement when compared with experimental data thereby proving the validity of the model. Ó 2006 Elsevier Ltd. All rights reserved. PACS: 85.30.De; 84.37.+q; 81.05.Ea; 84.90.+a Keywords: AlGaN/GaN MODFET; HEMT; Gate–source capacitance; Gate–drain capacitance; Cutoff frequency 1. Introduction Generally, the large band gap materials are suitable for fabrication of microwave high power devices [1]. The high electron mobility transistor [HEMT] fabricated in AlGaN/ GaN materials is most suitable for high power, high tem- perature microwave devices. The most important device characteristics for microwave power applications are breakdown voltage, current carrying capability and speed [2,3]. GaN has a high breakdown field (3 MV/cm) which is much larger than that of GaAs. AlGaN/GaN HEMTs also have the advantage of two dimensional electron gas (2-DEG) similar to other HEMTs. The 3.4 eV band gap in GaN allows 7.5 times as much electric field as for GaAs before avalanche breakdown occurs. Moreover, the piezo- electric and spontaneous polarization effects results in a high density 2-DEG at the AlGaN/GaN hetero-interface [4–7]. Therefore, AlGaN/GaN can maintain much higher current densities than other III–V HEMTs. GaN has attractive electronic material properties like high peak and saturation carrier velocity (3 · 10 7 cm/s and 2 · 10 7 cm/s as compared to 2 · 10 7 cm/s and 10 7 cm/s of GaAs). A good thermal conductivity (1.3 W/cm as compared to 0.5 W/cm of GaAs). These superior properties of GaN are adequate for power applications despite of its high effective electron mass (0.22 m e ) and small low field mobil- ity’s compared to AlGaAs. Strong lattice polarization effects, due to piezoelectric and spontaneous polarization fields present in GaN based materials, leads to a sheet car- rier concentration of (10 12 –10 13 cm 3 ) or higher. Presence of large polarization field at the hetero-interface produces strong conduction band bending and an increased carrier confinement [8–10] which accounts for high value of sheet 0038-1101/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.sse.2006.11.002 * Corresponding author. Tel.: +91 11 24115580; fax: +91 11 24110606. E-mail addresses: gangwaniparvesh@yahoo.com (P. Gangwani), rsgu@bol.net.in (R.S. Gupta). www.elsevier.com/locate/sse Solid-State Electronics 51 (2007) 130–135