Naujienos ir renginiai

Kviečiame į Saulėtekio puslaidininkių fizikos seminarą:

Intrinsic ballistic nanostructures
Roman Sobolewski (University of Rochester, USA)

2019-05-28 16:00 / NFTMC D401, Saulėtekio al. 3, Vilnius

Pranešimo anotacija (anglų. k.):
Intrinsic nanostructures exhibit unique physical properties that are a direct consequence of their nano-scale parameters and the quantum mode of operation, in contrast to scaled down versions of well-known conventional devices. One of the best-known examples is a nonlinear, asymmetric nano-channel diode (ANCD), also called self-switching diode (SSD), invented in 2004 by Song et al. Unlike conventional, e.g., p-n diodes, the ANCD performance is not based on a vertical structure and the junction barrier, instead, it produces diode-like characteristics through nonlinear carrier transport in depletion-controlled nano-channel. The ANCD planar geometry allows for a flexible design and easy integration as multi-element sensors. Indeed, ANCDs have been demonstrated to be viable THz detectors and, based on Monte Carlo simulations, are expected to be efficient THz generators. We present our studies on fabrication and electrical and optical characterization of semiconducting ANCDs, focusing on the electron transport mechanism in a nano-channel, as well as their optical photoresponse. Our test devices were fabricated in InGaAs/InAlAs and GaAs/AlGaAs heterostructures with a 2-dimensional electron gas (2DEG) layer and patterned using electron beam lithography. Typical devices exhibit 250-nm–wide and 70-nm–deep trenches, defining a 2-μm–long and 230-nm-wide nano-channel. The ANCD I-V curves collected in the dark showed nonlinear, diode-type behavior at all tested temperatures. At high temperatures, they could be well fitted to the diode equation with a thermionic barrier, while below 100 K the carrier transport was temperature independent and dominated by tunneling of carriers within a 2DEG nanochannel across a parabolic potential barrier. In all of our devices, the impact of the light illumination was very clear, and there was a substantial photocurrent, even for incident optical power as low as 1 nW. The magnitude of the optical responsivity in ANCDs increased linearly over many orders of magnitude with the decrease of the optical power, reaching well above 1000 A/W at 1-nW excitation. This ultrahigh photoresponse was even further enhanced at low temperatures and at 78 K the responsivity was on the order of 10⁴ A/W at nW-level optical excitation. The latter indicates that with the strongly suppressed dark current at low temperatures, cryogenic ANCDs look promising as candidates for single-photon–level optical detectors.

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