Microwave performance of double δ-doped high electron mobility transistor with various lower/upper planar-doped ratio designs

The microwave noise, power, and linearity characteristics of pseudomorphic high electron mobility transistors (pHEMTs) with various lower/upper planar δ-doped ratios were systematically evaluated and studied. By varying the lower/upper δ-doped ratio from 1:1 to 1:4, both Schottky gate turn-on voltage V_ON and breakdown voltage V_BR were reduced. In addition, higher upper δ-doped design is effective in improving the device current density, transconductance, output power, and power-added efficiency; however, this design also scarified the flatness of transconductance distribution and Schottky performance, resulting in a degradation of device linearity. As to the noise performance, after increasing the upper δ-doped concentration by more than 2 × 10¹² cm^-2, the minimum noise figure NF_min can be reduced to a stable range, and higher current density cannot efficiently improve the noise performance. Although the 1:4 design provided the largest power density of pHEMT, its high gate leakage current at high input power swing limited its linearity, and 1:3 design achieved the best linearity performance.