The authors have studied the growth of bulk, freestanding zinc-blende (cubic) GaN layers by plasma-assisted molecular beam epitaxy (PA-MBE). They have established that the best structural properties of freestanding zinc-blende GaN can be achieved with initiation under Ga-rich conditions but without Ga droplet formation. It is difficult to initiate the growth of zinc-blende GaN, but it is even more difficult to sustain the growth of the pure zinc-blende polytype in thick layers without any wurtzite inclusions. In order to grow high quality freestanding cubic GaN layers, it is necessary to maintain the same growth conditions for about 1week. The best quality zinc-blende phase GaN was achieved in the first 10μm of the GaN layers. The authors have produced zinc-blende GaN substrates from our thick bulk GaN layers and they used the side previously attached to the GaAs substrate as the episide of these zinc-blende GaN substrates. They have demonstrated the scalability of the process by growing zinc-blende GaN layers on 2 and 3in. diameter wafers. The growth of freestanding bulk GaN layers has allowed them to refine the value for the lattice parameter of zinc-blende GaN as 4.510±0.005Å. They have demonstrated that the PA-MBE process developed has allowed them to grow freestanding AlxGa1−xN wafers.
Measurements of the current-voltage characteristics of zinc-blende (cubic) Al0.3Ga0.7N/GaN, double barrier resonant tunneling diodes are presented. Clear and reproducible negative differential resistance effects are observed, with room temperature peak-to-valley ratios up to 4 and peak currents up to about 1000 A cm−2.
Using the technique of picosecond acoustics, we measure the basic elastic and optical properties of a micrometre-thickness zinc-blende (cubic) GaN epitaxial film grown on GaAs. We provide low temperature values of the speed of sound, c11 elastic constant and refractive index. Our value of the elastic constant is in good agreement with the theoretical calculations for cubic GaN (Wright 1997 J. Appl. Phys. 82 2833).
In this review, the concept of open
cavity lasing for ultrasensitive
sensing is explored, specifically in driving important innovations
as laser-based biosensorsa field mostly dominated by fluorescence-based
sensing. Laser-based sensing exhibits higher signal amplification
and lower signal-to-noise ratio due to narrow emission lines as well
as high sensitivity due to nonlinear components. The versatility of
open cavity random lasers for probing analytes directly which is ultrasensitive
to small changes in chemical composition and temperature fluctuations
paves the path of utilizing narrow emission lines for advanced sensing.
The concept of random lasing is first explained followed by a comparison
of the different lasing threshold that has been reported. This is
followed by a survey of reports on laser-based sensing and more specifically
as biosensors. Finally, a perspective on the way forward for open
cavity laser-based sensing is put forth.
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