Peter S. Lyman

Photoluminescence characterization of pseudomorphic modulation‐doped quantum wells at high carrier sheet densities

A systematic study has been made of the photoluminescence spectra of modulation‐doped strained‐layer quantum wells at high electron sheet densities. Peaks associated with both the n=1 and n=2 electron subbands are observed, and the relative intensities are shown to be a result of the symmetry properties of the quantum wells. It is demonstrated that only the full width half maximum of the n=2 subband peak is useful for characterizing high carrier densities.

Improved pseudomorphic high electron mobility transistor structures on InGaAs substrates

Single and double pulse doped pseudomorphic high electron mobility transistor structures with 110-A-thick InGaAs channel layers have been grown on InxGa1−xAs substrates (x=0.04; 0.065) and GaAs substrates. For In0.23Ga0.77As channel layers, higher electron mobilities were obtained on In0.04Ga0.96As substrates due to reduced strain. Transmission electron microscopy micrographs on a GaAs-based sample exhibited a roughened selectively doped heterojunction but no detected misfit dislocations. Pseudomorphic structures with In0.27Ga0.73As channel layers were also grown on In0.065Ga0.935As substrates with good transport and optical properties. The properties of the analogous structure grown on GaAs were severely degraded. Transmission electron microscopy micrographs on the GaAs sample showed a very rough selectively doped heterojunction with misfit dislocations.

Highly uniform AlGaN/GaN HEMT films grown on 200-mm silicon substrates by plasma molecular beam epitaxy

Highly uniform AlGaN/GaN HEMT films with good electron transport properties have been grown on 200-mm silicon substrates by plasma molecular beam epitaxy. X-ray diffraction measurements indicate an AlGaN compositional and thickness variation of ±1% across the wafer, and a 29 point resistance map of a HEMT yielded a sheet resistance of 451 Ω/sq ± 1.1%. The electron mobility for seven measurements taken across the diameter of the wafer was 1555 cm2/Vs ± 1%. The mobility obtained on 200-mm silicon is within 10% of the mobility obtained for GaN HEMTs grown on 100-mm SiC substrates, which have a much smaller lattice mismatch with GaN. The uniform films were obtained at GaN growth rates comparable to 100-mm growth and a chamber pressure well within the free molecular flow regime.

Precise determination of indium composition and channel thickness in pseudomorphic high electron mobility transistors using room temperature photoluminescence

Proper composition and thickness of the InGaAs channel in pseudomorphic high electron mobility transistors (PHEMTs) is critical to assuring good device performance. Typically these characteristics have been measured by high-resolution x-ray diffraction. The results presented in this work show that the subband energy levels obtained from line shape analysis of room temperature photoluminescence spectra on these structures can be correlated very well with thickness and composition obtained from x-ray diffraction. Since the photoluminescence measurement and analysis is quite fast, this technique is suitable for rapid, nondestructive screening of PHEMT epitaxial material.

ALGAAS/INGAAS/ALGAAS DOUBLE PULSE DOPED PSEUDOMORPHIC HIGH ELECTRON MOBILITY TRANSISTOR STRUCTURES ON INGAAS SUBSTRATES

Double pulse doped AlGaAs/InGaAs/AlGaAs pseudomorphic high electron mobility transistor (PHEMT) structures have been grown on InxGa1−xAs (x=0.025–0.07) substrates using molecular beam epitaxy. A strain compensated, AlGaInAs/GaAs superlattice was used for improved resistivity and breakdown. Excellent electrical and optical properties were obtained for 110-A-thick InGaAs channel layers with indium concentrations up to 31%. A room temperature mobility of 6860 cm2/V s with 77 K sheet density of 4.0×1012 cm−2 was achieved. The InGaAs channel photoluminescence intensity was equivalent to an analogous structure on a GaAs substrate. To reduce strain PHEMT structures with a composite InGaP/AlGaAs Schottky layer were also grown. The structures also exhibited excellent electrical and optical properties. Transmission electron micrographs showed planar channel interfaces for highly strained In0.30Ga0.70As channel layers.