Lecture 4 Carrier Transport Phenomena

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Presentation transcript:

Lecture 4 Carrier Transport Phenomena DMT 234 Semiconductor Physic & Device Lecture 4 Carrier Transport Phenomena Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device Preview The net flow of the electron and holes in a semiconductor will generate current. The process which these charged particles move is call transport. Two basic transport : Drift & Diffusion. The carrier transport phenomena are the foundation for finally determining the current-voltage characteristics of semiconductor devices. Subtopic : Carrier Drift Carrier Diffusion Hall Effect. Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1 Carrier Drift Transport : The process which charged particles ( holes or electrons) are move. Understanding of the electrical properties ( I-V properties) Basic current Equation : Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.1 Drift Current Density Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.1 Drift Current Density Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.1 Drift Current Density Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.1 Example carrier drift To calculate the drift current density in a semiconductor for a given electric field. Consider a gallium arsenide sample at T=300K with doping concentration of Na = 0 and Nd = 1016 cm-3. Assume complete ionization and assume electron and hole mobilities given is un = 8500 cm2/v-s and up = 400 cm2/v-s. Calculate the drift current density if the applied electric field is E = 10 V/cm. Since Nd > Na, the semiconductor is n type and the majority carrier electron concentration: n = Nd – Na / 2 + √ ( Nd- Na/ 2)2 + ni2 = 10 16 cm-3 The minority carrier hole concentration is : p = n2i / n = (1.8 x 106)2 / 1016 = 3.24 x 10-4 cm-3 For this extrinsic n-type semiconductor, the drift current density is : Jdrf = e ( unn + upp)E = eunNdE Then , Jdrf = (1.6 x 10-19)(8500)(1016)(10) = 136 A/cm2 Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.2 Mobility Efects Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.2 Mobility Effects Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.2 Mobility Effects Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.2 Mobility Effects Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.2 Mobility Effects Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.2 Mobility Effects Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.2 Mobility Effects Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.2 Mobility Effects Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.2 Mobility Effects Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.2 Mobility Effects Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.3 Conductivity Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.3 Conductivity Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.3 Conductivity Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.3 Conductivity Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.1.3 Velocity Saturation Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.2 Carrier Diffusion Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.2 Carrier Diffusion Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.2 Carrier Diffusion Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.2 Carrier Diffusion Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.2 Example Carrier Diffusion To calculate the diffusion current density given a density gradient. Assume that, in an n-type gallium arsenide semiconductor at T= 300 K, the electron concentration varies linearly from 1 x 1018 to 7 x 1017 cm-3 over a distance of 0.10 cm. Calculate the diffusion current density if the electron diffusion coefficient is Dn = 225 cm2/s. The diffusion current density is given : Jn|dif = eDn dn/dx = (1.6 x 10-19)(225)(1 x 1018 – 7x1017/0.1) = 108 A/cm2. Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.2.1 Total current density Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.2.1 Einstein relation Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.2.1 Einstein relation Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.2.1 Einstein relation Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.3 Hall Effect Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.3 Hall Effect Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.3 Hall Effect Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.3 Hall Effect Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device 4.3 Example Hall Effect To determine the majority carrier concentration and mobility, given Hall effect parameters. Consider the geometry shown in Figure from previous slide. Let L = 10-1 cm ,W = 10-2 cm, and d = 10-3 cm. Also assume that Ix = 1.0 mA, Vx = 12.5 V, Bz = 500 gauss = 5 x 10-2 tesla and VH = -6.25 mV. A negative Hall voltage for this geometry implies that we have an n-type semiconductor using equation, we can calculate the electron concentration as : n = -(10-3)(5 x 10-2)/ (1.6 x 10-19)(10-5)(-6.25 x 10-3) = 5 x 1021 m-3 = 5 x 1015 cm-3 The electron mobility is then determine from equation as : Un = (10-3)(10-3) / (1.6 x 10-19)(5 x 1021)(12.5)(10-4)(10-5) = 0.1 m2/ V-s Or Un = 1000 cm2/V-s. Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device Q & A Next week Topic :Nonequilibrium Excess Carriers in Semicondcutor. Mnorhafiz 2011

DMT 234 Semiconductor Physic & Device Mnorhafiz 2011