Effect of temperature on the transconductance of AlGaN/GaN high electron mobility
transistors (HEMT)
Rajab yahyazadeh1, Zahra Hashempour1, Lyla shrifzadeghan2 and Roghaye ahmadi2
Department of Physics, Islamic Azad University, Khoy branch, Khoy 58135/175, Iran
Department of Physics, Islamic Azad University, Central Tehran branch
An analytical-numerical model for the electronic current of two dimensional quantum well AlGaN/GaN in
high electron mobility transistors has been developed in this paper that is capable of accurately predicting
the effect of temperature on the electronic current of two dimensional quantum well
and
transconductance . Salient futures of the model are incorporated of fully and partially occupied sub-bunds
in the interface quantum well .In addition temperature dependent of band gap , quantum well electron
density , threshold voltage, mobility of electron , dielectric constant , polarization induce charge density in
the device are also take in to account . In order to obtain accurate values for the Fermi energy, the
energies of quantized levels within the two dimensional electron gas (2DEG), the occupancy of the
various sub-bands, the intrasub-band and intersub-band coupling coefficients (Hmn) for the two
dimensional electron gas in AlGaN/GaN heterostructures; both the Schrödinger and Poisson equations
must be solved self-consistently. This has been achieved by solving Schrödinger’s equation
and
simultaneously taking into account the electrostatic potential obtained from Poisson’s equation, as well as
the image and exchange-correlation potentials using Numerov’s numerical method.
In the self-consistent calculation, the nonlinear formulism of the polarization–induced field as a function
of Al mole fraction in AlmGa1-mN/GaN heterostructures has been assumed, as well as taking in to account
all fully and partially–occupied sub-bands within the interface two dimensional electron gas potential well
[1, 2]. Using such an approach, it is possible to calculate the two dimensional electron mobility taking into
account the combined contributions from each of the individual electron scattering mechanisms. At high
temperature (T ≥ 300K), inelastic polar optical phonon scattering dominates over all other scattering
mechanisms. In the linearized Boltzmann equation, the different scattering rates can be separated in to
two type: (i) elastic scattering du to acoustic and piezoelectric phonons, ionized impurities and interface
roughness, etc., and (ii) inelastic scattering due to polar optical phonons in order to take in to
consideration all scattering mechanism in the mobility calculation, it is solve numerically using an iterative
technique [3]. The small signal parameter such as the transconductance, g m , can be define by differentiating
of I DS with respect to V gs keeping respectively V ds constant.[4]
gm 
 ( I 2 DEG  I AlGaN )
VGS
V
DS cons tan t
 g m ( 2 DEG)  g m ( AlGaN)
1
In this model, the channel temperature varies at each operating point depending on the device power [18,26]:
Tch  T0  I DSVDS Rth
Where
2
Rth is the thermal resistance which is dependent on temperature.Fig. 1 shows the DC
transconductance as a function of the gate to-source biasing at different temperatures. This proposed
model quite accurately predicts the overall trend of the transconductance. The calculated model results
are in very good agreement with existing experimental data for high electron mobility transistors device.
References:
[1]. M.A.Huque, S.A.Eliza, T.Rahman, H.F.Huq, S, K.Islam;" Temperature dependent analytical model for current –
voltage characteristics of AlGaN/GaN power HEMT" Solid – Stat Electronics 53 (2009)341
[2].E. J. Miller, X. Z. Dang, H. H. Wieder, P. M. Asbeck, and E. T. Yu, J. Appl. Phys. 87, 8070 (2000).
[3].G. Koley, V. Tilak, Ho-Young Cha, L. F. Eastman, and M. G. Spencer, IEEE Electron Device Letters, 8, 473
(2002).
[4]Z. Hashempour, A. Asgari, S. Nikipar, M. R.Abolhasani, M. Kalafi, Numerical performance evaluation of
AlGaN/GaN high electron mobility transistor including gate length effects, Phisica E, 41 (2009) 1517-1521.
[5].M.Li,Y.Wang, " 2--D analytical Model for Current-Voltage Characteristics and Transconductance Of
AlGaN/GaN",IEEE Trans,on Electron Devices Vol.55,No.1,Jun (2008) 261-26
Fig.1 shows the variation of transconductance and total drain source current as function of gate source voltage
Al0.5Ga0.5N/GaN HEMTs in 300K and 400k. The dot represents Exp. Data from Ref. [5].
for the