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Sheet charge Density Arpan Deyasi Further integrating Nanoelectronic −  −  d d q  = − Device −  =  − ( ) ( 0) ( ') ' z d z d dz N z dz  − − b ds ds q V z − = − ) 0 − =  − − 2 ( ( ) d d N d d D s  b Arpan Deyasi, India 14 Sheet charge Density Arpan Deyasi Integrating Nanoelectronic z   d dz Device d dz q = −  − ( ') ' N z dz  ' ' = 0 z z b 0 z   d dz q = − −  ( ') ' N z dz  ' z b 0 Arpan Deyasi, India 13 Sheet charge Density Arpan Deyasi Poisson’s equation is barrier region Nanoelectronic ( ) qN z    = − 2 Device b −  −  d z d = ( ) N z N where s 0 D   sd z N z = ( ) 0 Arpan Deyasi, India 12 Sheet charge Density Arpan Deyasi From Gauss law Nanoelectronic   = qn b s dielectric of barrier region Device Arpan Deyasi, India 11

Sheet charge Density Arpan Deyasi Φb: barrier height of Schottky barrier gate ds: spacer layer distance d: gate-to-channel distance Device Nanoelectronic ξ: electric field at the interface region of barrier ns: 2-DEG density Arpan Deyasi, India 10 Materials used in HEMTs Arpan Deyasi GaAs: used in the first HEMTs Nanoelectronic GaN: an improvement upon the GaAs based HEMTs InP: used in some of the most advanced HEMTs Device Arpan Deyasi, India 8īand Diagram Arpan Deyasi qφb Nanoelectronic Device ΔEC qVG z=0 z=-ds z=-d z Arpan Deyasi, India 9 So the device is treated as high-gain, low-noise one Arpan Deyasi, India 6Ĭharacteristics of HEMT Arpan Deyasi Using materials with higher conduction band discontinuity, large device transconductance can be obtained Nanoelectronic Because of smaller active channel, it can be operated at lower temperature Device Arpan Deyasi, India 7 Structure Arpan Deyasi Source Drain Nanoelectronic n+GaAs n+ GaAs Gate Device n+ AlGaAs n+ AlGaAs Undoped AlGaAs spacer layer GaAs 2DEG Semi-insulating substrate Arpan Deyasi, India 5Ĭharacteristics of HEMT Arpan Deyasi mobility of free carriers are very high due to suppressed ionized impurity scattering which makes very low gate-to-source resistance Nanoelectronic Device carrier freezeout problem is not present at extremely low temperature because of electrons presence in a region of energy below donor levels in high bandgap material. Solution of problem Arpan Deyasi Separate the two Nanoelectronic How? Doping is done in one region and Mobile carriers will subsequently migrate Device into another region Process is known as modulation doping Arpan Deyasi, India 3Ĭarrier separation Arpan Deyasi Ionized donors Metal Nanoelectronic Metal Free Device electrons Undoped AlGaAs buffer AlGaAs donor layer GaAs well Arpan Deyasi, India 4 Problems in conventional transistor Arpan Deyasi Scattering between donors/acceptors and mobile carriers Nanoelectronic D Impurity scattering Device M.C High noise Arpan Deyasi, India 2 Course: Nanoelectronic Device Arpan Deyasi High Electron Mobility Transistor Nanoelectronic Device Arpan Deyasi RCCIIT, India Arpan Deyasi, India 1