SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

3.5. SOME IMPORTANT ISSUES IN TRANSPORT 117 3.5 SOMEIMPORTANTISSUESINTRANSPORT ................. We will discuss some important ...

118 CHAPTER 3. CHARGE TRANSPORT IN MATERIALS Electron Energy (eV) GaN GaAs InGaAs Figure 3.14: Scattering rates in InGaAs, GaAs, ...

3.6. CARRIER TRANSPORT BY DIFFUSION 119 a) b) Figure 3.15: Temperature dependence of scattering rates in 2DEGs for (a) InGaAs an ...

120 CHAPTER 3. CHARGE TRANSPORT IN MATERIALS nR xo– xo x xo+ nL LR mean free path C ARRIER CONCENTRATION Figure 3.16: The concen ...

3.6. CARRIER TRANSPORT BY DIFFUSION 121 whereDnis called the diffusion coefficient of the electron system and depends upon the s ...

122 CHAPTER 3. CHARGE TRANSPORT IN MATERIALS E l ectri c f i el d E(x) Position in space, x UNIFORM ELECTRIC FIEL D (a) +ve –ve ...

3.6. CARRIER TRANSPORT BY DIFFUSION 123 individually zero and we have from equation 3.6.6 for the electrons E(x)=− Dn μn 1 n(x) ...

124 CHAPTER 3. CHARGE TRANSPORT IN MATERIALS Dn Dp μn μp (cm^2 /s) (cm^2 /s) (cm^2 /V •s) (cm^2 /V •s) Ge 100 50 3900 1900 Si 35 ...

3.8. CARRIER GENERATION AND RECOMBINATION 125 different hole Fermi level). We then have n= ∫∞ Ec Ne(E)fe(E)dE (3.7.1) p= ∫Ev −∞ ...

126 CHAPTER 3. CHARGE TRANSPORT IN MATERIALS – – – – + + Ec Equilibrium Fermi level for an n-type material Ev Excess electron in ...

3.8. CARRIER GENERATION AND RECOMBINATION 127 – –––––– Ec Band to band electron-hole generation Ev +–– – – ––– – ––––– – donor i ...

128 CHAPTER 3. CHARGE TRANSPORT IN MATERIALS + Absorption Photon ABSORPTION (a) (b) Photon EMISSION “Vertical” in k – Emission – ...

3.8. CARRIER GENERATION AND RECOMBINATION 129 These processes are controlled by the conservation laws. Conservation of energy: ...

130 CHAPTER 3. CHARGE TRANSPORT IN MATERIALS (^10) 0.2 0.6 1 1.4 1.8 106 105 104 103 102 32 1.5 1 0.7 PHOTON ENERGY (eV) WAVELEN ...

3.8. CARRIER GENERATION AND RECOMBINATION 131 electron-hole system and is Ncv(E)= √ 2(m∗r)^3 /^2 (E−Eg)^1 /^2 π^2 ^3 (3.8.9) If ...

132 CHAPTER 3. CHARGE TRANSPORT IN MATERIALS iii)Weak injection:In this case we can use the Boltzmann distribution to describe t ...

3.8. CARRIER GENERATION AND RECOMBINATION 133 3.8.2 Schockley Read Hall Statistics ...................... Semiconductor behavior ...

134 CHAPTER 3. CHARGE TRANSPORT IN MATERIALS σn[cm-2] Trap Figure 3.23: Picture of the capture cross section Case 1 vth x 0 Case ...

3.8. CARRIER GENERATION AND RECOMBINATION 135 whereEis thermal energy, 3 / 2 kBTin three dimensions. Thus vth= √ 3 kBT m∗ 107 c ...

136 CHAPTER 3. CHARGE TRANSPORT IN MATERIALS GL ra rb rc rd Figure 3.25: Possible Recombination processes or the net capture rat ...