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TECHNICAL
STRATEGY |
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Spectroscopy of group III-nitrides |
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We will continue the development of collection-mode near-field optical methods and examine the group III-nitrides using second-harmonic generation and photoluminescence (PL) spectroscopies on a resolution scale of 20 to 100 nm. Time-resolved photoluminescence is also a very important metric for examining material quality in the III-nitrides. We have put more emphasis on capablilites in time-resolved PL and applying this tool to both nanowires and thin-film III-nitrides. Additionally, we have recently added spectrally resolved photoconductivity to our suite of spectroscopy tools for examining nitride films and nanowires. This technique has proved important for the examination of persistent photoconductivity in these materials, the evaluation of alloy composition, and the development of Schottky, p-i-n, and heterojunction quantum well devices in nanowires. |
| Electrically addressable optoelectronic nanowires |
| We will fabricate UV-blue LEDs and lasers from SQNWs. The SQNWs will be grown in the group III-nitride semiconductor system by plasma-assisted MBE and/or chemical beam epitaxy. Required attributes include high purity, low defect density, the ability to engineer heterostructures and make electrical contact, and precise doping control. A suite of test structures will be developed that will include intrinsic, p- and n-doped wires, “core-sleeve,” and axially alternating junction/heterostructures of SQNWs. We will develop new techniques for selective area growth and apply these methods to the patterned growth of SQNWs. We will optimize techniques to form electrical contact individually or to arrays of SQNWs. We will use AFM, XRD, TEM, FESEM, Raman spectroscopy, and electron-backscattering diffraction (EBSD) for the structural characterization in this work. Contact: Dr. Norman Sanford |
| Refractive index measurements of group III-nitrides |
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have compiled refractive index and birefringence data for a number of AlGaN samples ranging in composition from pure GaN to Al0.66Ga0.24N, using prism coupling to waveguide mode techniques that are correlated with spectroscopic reflection and transmission measurements (performed by collaborators in MSEL). Furthormore, the Al mole fraction of this sample set was separately determined by analytical electron microscopy. We also have measured refractive index of InGaN for low In mole fractions of technological interest. Contact: Dr. Norman Sanford |