Non-Contact Determination of Free Carrier Concentration in n-GaInAsSb
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Non-Contact Determination of Free Carrier Concentration in n-GaInAsSb James E. Maslar1, Wilbur S. Hurst1, Christine A. Wang2, and Daniel A. Shiau2 National Institute of Standards and Technology, Gaithersburg, MD 20899-8360 2 Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, MA 02420-9108 1
ABSTRACT GaSb-based semiconductors are of interest for mid-infrared optoelectronic and high-speed electronic devices. Accurate determination of electrical properties is essential for optimizing the performance of these devices. However, electrical characterization of these semiconductors is not straightforward since semi-insulating (SI) GaSb substrates for Hall measurements are not available. In this work, the capability of Raman spectroscopy for determination of the majority carrier concentration in n-GaInAsSb epilayers was investigated. Raman spectroscopy offers the advantage of being non-contact and spatially resolved. Furthermore, the type of substrate used for the epilayer does not affect the measurement. However, for antimonide-based materials, traditionally employed Raman laser sources and detectors are not optimized for the analysis wavelength range dictated by the narrow band gap of these materials. Therefore, a near-infrared Raman spectroscopic system, optimized for antimonide-based materials, was developed. Ga0.85In0.15As0.13Sb0.87 epilayers were grown by organometallic vapor phase epitaxy with doping levels in the range 2 to 80 x 1017 cm-3, as measured by secondary ion mass spectrometry. For a particular nominal doping level, epilayers were grown both lattice matched to n-GaSb substrates and lattice-mismatched to SI GaAs substrates under nominally identical conditions. Single magnetic field Hall measurements were performed on the epilayers grown on SI GaAs substrates, while Raman spectroscopy was used to measure the carrier concentration of epilayers grown on GaSb and the corresponding SI GaAs substrates. Contrary to Hall measurements, Raman spectra indicated that the GaInAsSb epilayers grown on GaSb substrates have higher free carrier concentrations than the corresponding epilayers grown on SI GaAs substrates under nominally identical conditions. This is contrary to the assumption that for nominally identical growth conditions, the resulting carrier concentration is independent of substrate, and possible mechanisms will be discussed. INTRODUCTION GaSb-based group III-V semiconductors are of interest for mid-infrared sources and detectors and low-power, high-speed electronic devices [1]. Of this class of materials, Ga1-xInxAsySb1-y, with a composition-dependent direct energy gap in the wavelength range from 1.7 µm (0.726 eV) to 4.2 µm (0.296 eV), has been used to fabricate a variety of optoelectronic devices operating in the mid-infrared wavelength range [2]. Accurate determination of electrical properties is essential for optimizing the performance of such devices. However, electrical characterization of GaInAsSb devices grown lattice-matched to GaSb is complicated by the scarcity of semi-
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