Schematic of the grating-gated InP-based HEMT. The epitaxially grown materials are indicated as A = In0.48Al0.52As with δ-doping at the interface with B, B = undoped In0.48Al0.52As spacer, C = In0.32Ga0.68As channel, and E = In0.48Al0.52As buffer layer. Radiation is incident on the grating-gate from the left. The black curve, calculated by finite element method (Silvaco Atlas), indicates the charge density distribution.
Optical microscope image of the grating gated InP-based HEMT.
Schematic of the experimental setup.
Calculated absorptance spectra for three different grating periods of 9, 2, and 0.5 μm. Fundamental and harmonics are labeled in each spectrum.
(a) Calculated absorptance spectra. Absorptance maxima are marked by symbols. (b) Calculated dA/df spectra. The horizontal bars indicate the available BWO ranges.
Photoresponse of the HEMT at T = 4 K to mm-wave radiation for three gate biases. Data are for nominal perpendicular polarization as expected from the horn orientation (inset schematic).
Comparison of theoretical dA/df curves with linear fits to measured photoresponse data for nominal perpendicular polarization. The upper (lower) group of curves corresponds to the upper (lower) frequency axis.
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