compound semiconductors ps2015
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Compound Semiconductors problemsTRANSCRIPT
Compound Semiconductors- Properties & ApplicationsProblem Sheet
1. (a) A GaAs MESFET channel is doped with a concentration of ND = 1017/cm3. If the Schottky barrier height ((B) = 0.8 V, what is the built-in potential?
(b) Calculate the pinch-off voltage and the threshold voltage if the channel thickness is
(i) 250 nm, (ii) 150 nm
(c) If the channel length (L) = 250 nm and channel width is 2 m, calculate the saturation current, when VGS Vth =1.0V assuming
(i) current saturation due to pinch-off
(ii) Michael Shurs formula valid for all values of (2. An Al0.2Ga0.8As/GaAs HEMT has the following specifications: Doping concentration in AlGaAs = 1018/cm3, Schottky barrier height ((B) = 0.9 V, channel width =50 m, (a)What should be the AlGaAs layer thickness such that the Threshold voltage of the HEMT is 0.15 V? Assume spacer layer thickness = 0
(b) How will the threshold voltage change if a spacer layer of thickness 5 nm is incorporated in the above structure keeping the total AlGaAs layer thickness unchanged?
(c) What will be the maximum intrinsic transconductance in the two above cases of (b) and (c)?
3. For an AlGaN/GaN system, assuming that there exists a single donor like surface state 1.65 eV below the conduction band edge of AlGaN, what should be the thickness of the AlGaN layer in order to realize a 2DEG concentration of 1013/cm2? Assume the concentration of bound charge ((b) = 1.5 x1013/cm2.
[Assume that the value of (Ec = 0.5 eV and the relative permittivity of AlGaN = 9 for this system; (0 = 8.854 x 10-14 F/cm]
4. Consider an n-Al0.3Ga0.7AS/pGaAs abrupt heterojunction with doping concentrations of ND = 1017/cm3 and NA = 1019/cm3.
(a) Calculate the built-in potential
(b) At zero bias, what are the depletion layer widths and the potential drops on the n and p sides?
(c) When the junction is forward biased by 1.3V, what are the potential drops on the n and p sides?
[Given : For AlxGa1-xAs, Eg = 1.425 +1.155x +0.37x2; ( = 4.07 -0.62 (1.155x +0.37x2); ( = 12.9-2.9x.For both GaAs and AlGaAs, assume, Nc = 4.7 1017/cm3, Nv = 7 1018/cm3, n = 3000 cm2/Vs, p = 250 cm2/Vs, vsat = 1107 cm/s.]