Resonant electron tunneling in single quantum well heterostructure junction of electrodeposited metal semiconductor nanostructures using nuclear track filters
Introduction
The technological importance of Nuclear Track Filters (NTFs) is very large due to the various potential applications particularly in the field of micro/nanostructure electronic device fabrication. In recent years, there has been tremendous interest in nanopores and micropores in polymers, generated by swift heavy ions (SHI) due to a vast variety of applications [1], [2]. These pores are created by controlled chemical etching of ion-irradiated thin polymer foils, so as to produce NTFs. Physical properties of a material can change significantly in the transition between the macroscopic scale and the nanoscale. Therefore, nanophysics fabrication is very important both for its technological application and fundamental interest. The possibility of resonant tunneling in a zero-dimensional quantum well has been the subject of intense research over the years, since the first work by Reed et al. [3]. Functional devices based on resonant tunneling through double barrier heterostructures are of much promise in a variety of applications such as digital and analog circuits. However, a single barrier structure being easy to fabricate and of better high-frequency response is also of much interest. To date, most of the research on small area resonant tunneling devices has employed AlGaAs–GaAs heterostructure semiconducting material systems, which have been grown by Molecular Beam Epitaxy (MBE) technique followed by reactive ion etching [4], [5], [6]. Fabrication of resonant tunnel devices using the MBE technique has certain limitations as reactive ion etching can introduce damage at the device side wall surface [7]. However, recent advances in electrodeposition technique make possible the growth of well-defined periodic structures, such as magnetic multilayers with layer thicknesses as small as few nanometers [8]. Chakarvarti et al. [9], [10] recently employed this relatively easy and versatile electrodeposition technique to grow microstructure metal-semiconductor heterostructure junctions using the novel material system Cu–Se in the chemically etched pores of polycarbonate foils. The first and preliminary investigation on this entirely new and until now unpublished material system demonstrated characteristic feature for the formation of a microstructure resonant tunneling diode [10]. In this paper, we present results of our detailed investigation on the array of low-dimensional resonant tunneling diodes (RTD), fabricated by controlled electrodeposition of Cu–Se in the nanopores of a swift heavy ion-irradiated polycarbonate foil. We also demonstrate a low-cost resonant tunneling device as a result of a metal semiconductor (Cu–Se) single barrier heterostructure, which provides negative differential resistance (NDR) characteristic with high peak to valley current ratio (PVR) even at room temperature.
Section snippets
Experimental details
The NTFs used in the present work were of Makrofol KG (polycarbonate from Bayer AG), 10 μm thick, having an average pore diameter of 800 nm with pore density 106 cm−2. These were prepared by irradiating the foils with heavy ions (28Si, 100 MeV with ion fluence 106 ions/cm2) at the 15 MV pelletron accelerator of the Nuclear Science Centre (NSC) [11] New Delhi, India, using the General purpose scattering chamber (GPSC) facility and followed by chemical etching of the latent tracks in 6.25 N NaOH,
Results and discussion
Fig. 3(a) and 3(b) show the scanning electron microscopy (SEM) pictures of the array of several RTDs fabricated as metal semiconductor nanostructures using NTF. For this SEM picture, the polymer matrix was dissolved in a suitable organic solvent, leaving behind the metal semiconductor nanostructure. Fig. 3(a) is the lateral view of several nanofabricated RTDs, in which the upper layer is copper and the lower layer is selenium. It seems that the polymer matrix is not fully removed by the organic
Conclusion
In conclusion, we report here on the observation of resonant tunneling in a Cu–Se single barrier/single quantum-well heterostructure junction produced electrochemically in the nanopores of nuclear track filter NTF (polycarbonate). We have demonstrated that in comparison to the high cost molecular beam epitaxy system, the easy and cheap electrodeposition technique can be a very effective way to prepare resonant electron tunneling devices using nanopores of NTFs. The current voltage
Acknowledgments
One of the authors (A.B.) is thankful to Prof. S.K. Chakarvarti of REC, Kurukshetra, for introducing the topic and providing him with films of polycarbonate and to Dr. Dhirendra Pal of Standard Appliances, Varanasi, for assisting in the fabrication of the electrodeposition cell.
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