Polarization-Induced GaN-on-Insulator E/D Mode p-Channel Heterostructure FETs

Abstract

Polarization-induced <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$p$</tex></formula> -type doping is realized in molecular beam epitaxy (MBE) grown ultrathin body GaN/AlN heterostructures. The novel heterostructure consisting of a thin strained GaN layer grown on an AlN template exhibits a hole gas density close to the interface polarization charge <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$({\sim}5\times 10^{13}/{\rm cm}^{2})$</tex></formula> . Both enhancement- and depletion-mode (E/D) p-channel heterostructure field effect transistor (HFETs) are demonstrated. Driven by the high hole density, a 2.4- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu{\rm m}$</tex></formula> -long D-mode HFET with alloyed ohmic contacts shows improvement of drain current from 150 mA/mm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$({\rm V}_{\rm GS}=12~{\rm V},{\rm V}_{\rm DS}=30~{\rm V})$</tex></formula> at 300 K to 270 mA/mm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$({\rm V}_{\rm GS}=15~{\rm V},{\rm V}_{\rm DS}=30~{\rm V})$</tex></formula> at 77 K. The extrinsic peak transconductance of the D-mode device increases from 11 mS/mm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$({\rm V}_{\rm GS}=6~{\rm V},{\rm V}_{\rm DS}=30~{\rm V})$</tex></formula> at 300 K to 16 mS/mm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$({\rm V}_{\rm GS}=4~{\rm V},{\rm V}_{\rm DS}=30~{\rm V})$</tex></formula> at 77 K. Both the drive current and transconductance are recorded in nitride p-channel FETs. MBE regrown heavily Mg-doped <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">${\rm p}^{+}$</tex></formula> -GaN is then employed for ohmic contacts of E-mode p-channel HFETs. A 2- <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$\mu{\rm m}$</tex></formula> -long E-mode device with a drain current of 4 mA/mm <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$({\rm V}_{\rm GS}=10~{\rm V},{\rm V}_{\rm DS}=80~{\rm V})$</tex></formula> and ON/OFF current ratio of <formula formulatype="inline" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex Notation="TeX">$10^{3}$</tex> </formula> is achieved.