A lightly doped deep drain GaAs MESFET structure for linear amplifiers of personal handy-phone systems

An improved GaAs MESFET structure, named a buried p-layer lightly doped deep drain (BP-LD3) structure, is proposed. This structure can be fabricated by the conventional self-aligned gate and selective ion implantation technologies, and the FET characteristics show a high transconductance, a high breakdown voltage, and a low drain-source resistance. The lightly doped deep drain characterizing this structure was introduced on the basis of a two-dimensional numerical analysis including an impact ionization for a buried p-layer lightly doped drain (BP-LDD) structure which has been applied for high-speed digital ICs. The simulated results clarified that a low breakdown voltage of the BP-LDD structure originates from a high rate of carrier generation due to the impact ionization in the lightly doped drain region. The reason is that both electric field and current density become high in the region. In the new BP-LD3 structure, the electron current expands due to the deep formation of lightly doped drain, therefore impact ionization is reduced. This BP-LD3 structure was fabricated and the FET characteristics were compared with those of the conventional BP-LDD structure, and a structure which is now being studied for linear amplifiers of 1.9 GHz personal handy-phone systems. The measured breakdown voltage of 8.1 V, transconductance of 360 mS/mm, and drain-source resistance of 2.5 /spl Omega//mm for the BP-LD3 structure indicate high potentiality for analog applications.