Demonstration of an amorphous carbon tunnel diode

Abstract

Negative differential conductance in metal/amorphous nitrogenated carbon ͑a-CN x ͒ / Si structures is demonstrated at room temperature. These metal-insulator-semiconductor tunnel diodes are fabricated by optimizing the tunnel barrier at the a-CN x / Si junction through the control of the band gap and nitrogen doping level in carbon where this a-C layer acts as a semi-insulator. A small electron tunneling effective mass of about 0.06 times the free electron mass, a coherence length of ϳ10 nm in these thin a-CN x layers and a low interface trap density suggest fast device operation similar to classical tunnel diodes. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2454512͔ Fabrication of tunnel junctions for fast devices has been attempted using a number of different graphitic carbon nanostructures including nanotubes, fullerenes, nanostructured amorphous carbon ͑a-C͒, and nanocrystalline diamond for large area electronics.1-5 However, it is somewhat surprising that the use of amorphous diamondlike carbon ͑DLC͒ films having high breakdown voltage and a low dielectric constant together with the high thermal stability for metal/insulator/ semiconductor ͑MIS͒ diodes and MIS transistors has not been fully explored. 5,6 Previously, by employing insulating DLC films or metallic graphitic films, heterojunctions have been created on crystalline silicon.6,7 However, charge accumulation at the interface or its leakage to the metal electrode without accumulation resulted due to the high defect density of states present in the films. 8 Hence, direct tunneling signatures in carbon MIS structures at low bias or strong charge inversion at high bias has not been reported. 5,[9][10][11][12][13][14][15] In practice, the well-known negative differential conductance in oxide based MIS tunnel diodes or transistors has been suppressed due to the contribution of a large density of interface trap states 16,17 and limits high frequency operation. We have recently demonstrated negative differential resistance in a-C quantum well structures. 18 In this letter, we explore the properties of a-CN x / Si devices grown at room temperature by carefully controlling the band gap, density of states at the Fermi level ͑E F ͒, and height of the tunnel barrier. In these a-CN x / Si heterostructures, we show features similar to those observed in state of the art direct tunnel devices with negative differential conductance. 16The samples were prepared by ablation of a high purity graphite target ͑99.99%͒ using a 248 nm pulsed UV excimer laser ͑Lambda Physik LPX 210i͒. By choosing different laser fluences ͑4 and 16 J / cm 2 ͒ and partial pressures of nitrogen ͑5 and 100 mT͒ in the deposition chamber, films A and B were fabricated. This gives a large variation of sp 3 bonded carbon and nitrogen doping levels in the samples, which helps control the band gap ͑E g ͒ in the range of 1 -2.5 eV, respectively. These samples, up to 20 nm thick, were deposited at room temperature on n-type Si ͑111͒ wafers ͑resistiv-ity ϳ0.01 ⍀ cm͒ to make a-CN x / Si heterost...

Evolution of the opto-electronic properties of amorphous carbon films as a function of nitrogen incorporation

“…In this way, a-CN x thin films are now being considered as a possible material to extend the applications of amorphous carbon materials which have presented limited success in electronic devices (OLEDs, TFTs…). The performance of such devices depends on the electronic properties of the films [3][4][5][6].…”

Structurally Driven Enhancement of Resonant Tunneling and Nanomechanical Properties in Diamond-like Carbon Superlattices

“…Keay et al have observed NDR behavior in GaAs superlattice structures and suggested that it occurs due to alignment and misalignment of sub band states under applied voltage. For carbon-based materials, Bhattacharyya and Silva have also found NDR behavior at room temprature for a-CN x /Si heterostructures, which becomes prominent at 80 K.…”

Enhanced tunnel transport in disordered carbon superlattice structures incorporated with nitrogen

“…6 Nevertheless, there have been efforts to establish the superior nano-electronic properties of nitrogen incorporated carbon heterostructures and related devices. [7][8][9] Although some interesting transport properties from the nitrogen incorporated carbon devices were observed, progress has been hindered by a limited understanding of the electronic transport mechanism in these structures. In general, the complex nature of defects in a À C and amorphous nitrogenated carbon (a À CN) films and their specific role in the possible enhancement of the electronic transport appear to be unresolved.…”

“…We think that the previously discussed models of disorder should have been extended for explaining quantum transport in a carbon system which could show the features of resonant tunneling. 5,7 Hence, it is fundamentally important to develop a microstructural model of a À C films based on the local distortion of sp 2 À C to sp 3 À C structures and the deformation potential of the respective bonds. 30 In multi-layered GaAs structures, the effect of disorder was shown by adjusting the hopping parameters and adding random potential fluctuations.…”