PHT.301 Physics of Semiconductor Devices

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Introduction

Electrons in crystals

Intrinsic Semiconductors

Extrinsic Semiconductors

Transport

pn junctions

Contacts

JFETs/MESFETs

MOSFETs

Bipolar transistors

Opto-electronics

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n-MESFET

The expression for the drain current of a n-channel MESFET is:

\[ \begin{equation} I_{D}=I_p\left[\frac{V_D}{V_p}-\frac{2}{3}\left(\frac{V_{bi}-V_G+V_{D}}{V_p}\right)^\frac{3}{2}+\frac{2}{3}\left(\frac{V_{bi}-V_G}{V_p}\right)^\frac{3}{2}\right] \end{equation} \]

Where the drain voltage $V_D$ and gate voltage $V_G$ are measured with respect to the source. The pinch-off voltage $V_P$ and pinch-off current $I_P$ are defined as,

\[ \begin{equation} V_P=\frac{eN_Dh^2}{2\varepsilon_0\varepsilon_r}, \end{equation} \] \[ \begin{equation} I_p=\frac{e^2_nN_D^2Zh^3}{2L\varepsilon_0\varepsilon_r}. \end{equation} \]

For a Schottky junction, the built-in voltage is,

\[ \begin{equation} eV_{bi}=\phi_b-k_BTln\left(\frac{N_c}{N_D}\left(\frac{T}{300}\right)^\frac{3}{2}\right) \end{equation} \]

Where $\phi_b$ is the Schottky barrier height. The equation above for the drian current is only valid if the MESFET is in the linear regime where $V_{D}\le V_p-V_{bi}+V_G$. For larger drain voltages, the drain current saturates to,

\[ \begin{equation} I_{D,sat}=I_p\left[\frac{1}{3}-\frac{V_{bi}-V_G}{V_p}+\frac{2}{3}\left(\frac{V_{bi}-V_G}{V_p}\right)^\frac{3}{2}\right]. \end{equation} \]
ID [mA]

VD [V]

 

$N_c=$

cm-3 @ 300 K

$N_v=$

cm-3 @ 300 K

$N_D=$

cm-3

$\phi_b=$

eV

$\mu_n=$

cm2/Vs

$h=$

μm

$L=$

μm

$Z=$

μm

$\epsilon_r=$

$T=$

K

$V_{D}$ (max)=

V

$V_g$ [1] =

V

$V_g$ [2] =

V

$V_g$ [3] =

V

$V_g$ [4] =

V

$V_g$ [5] =

V

$V_g$ [6] =

V

 


$V_{bi}=$  V;  $I_p=$  mA;  $V_p=$  V.