Carbon nanotubes (CNTs) were selectively grown in etched ion tracks in SiO 2 layers on Si . For this sake, Ni -catalyst nanocrystals were initially deposited within the ion tracks by galvanic deposition. The characteristics of plasma-enhanced chemical vapor deposition (PECVD)- and thermal chemical vapor deposition (TCVD)-grown CNTs, such as structural details and length distribution, were investigated. In addition, field emission properties were studied. The analysis revealed that the emerging PECVD-grown CNTs were of cylindrical and/or conical shape and usually had diameters as large as the etched tracks. The exponential length distribution of these CNTs can be well understood by applying a simple defect-growth model. For contrast, many narrow and curled CNTs were found to cluster in spots well separated from each other, after applying TCVD instead of PECVD. The Raman investigations of PECVD-grown CNTs showed that Si – O – C and Si – C phases had formed during the growth of the CNTs. These ion-track-correlated PECVD-grown CNTs open the way for the production of novel 3D nanoelectronic devices based on the TEMPOS concept. These structures are also excellent candidates for experiments on channeling in CNTs. Application as field emitting devices, however, appears unfavorable due to poor mean-field enhancement factors and insufficient stability.

Highly selective, low damage atomic layer etching ͑ALET͒ technology was developed for dry gate recess during the fabrication of InGaAs/ InP / InAlAs high electron mobility transistors lattice matched to InP substrates. Etching characteristics of InP layer on top of InAlAs layer and the surface chemistry of the exposed InAlAs layer were investigated by utilizing angular resolved x-ray photoelectron spectroscopy. Finally, InAlAs Schottky diodes were fabricated by utilizing chlorine-based ALET technology and conventional Ar-based dry recess and their electrical characteristics were compared. By using the ALET, the etch selectivity as high as 70:1 was achieved for InP over InAlAs heterostructures and the stoichiometric modification of InAlAs was observed to be negligible after the recess etch process. Schottky diodes fabricated after the ALET exhibited the lower ideality factor and the higher Schottky barrier height compared to those fabricated with Ar-based plasma etching.

Excitons in one-dimensional narrow gap semiconductors of anti-crossing quantum Hall edge states are investigated using a bosonization method. The excitonic states are studied by mapping the problem into a non-integrable sine-Gordon type model. We also find that many-body interactions lead to a strong enhancement of the band gap. We have estimated when an exciton instability may occur.PACS numbers: 71.27.+a, 71.35.Cc One-dimensional (1D) narrow gap semiconductors can be realized in anti-crossing quantum Hall edge states 1 and nanotubes 2 . The gaps in these systems are single particle gaps and not many body gaps. Theoretically, they provide the unusual condition that the bare band gap t is much smaller than the characteristic Coulomb energy scale E c . Moreover, strong quantum fluctuations are present in these systems, reflecting the 1D character. The ground state of these systems may be unstable against the spontaneous formation of excitons if the exciton binding energy exceeds the band gap 3,4 . In three dimensional semiconductors excitons can be treated successfully by solving the Bethe-Salpeter equation 4 . However, in the strong coupling regime of 1D systems, the perturbative approaches are not expected to be reliable due to large quantum fluctuations. If the Coulomb scale is much larger than the gap one might naively expect that exciton instability would occur. However, this simple picture neglects screening which is expected to be large due to the smallness of the gap. It is unclear whether a bound state of an "electron" and a "hole" can exists in the presence of strong quantum fluctuations. Not much is known about the physics of excitons in 1D narrow gap semiconductors.This problem can be addressed within a bosonization approach, which is applicable as long as the the characteristic energy scale of the problem is smaller than the band width W . Thus bosonization provides a natural framework for studying 1D excitons. In this work we will consider anti-crossing of quantum Hall edge states in the barrier region of between two 2D electron gases. Assume that the applied magnetic field is sufficiently strong that the system is spin-polarized with the filling factor ν = 1 and that the Fermi level is in the gap of anti-crossing edge states. We find that the problem can be mapped into a sine-Gordon (sG) model with an extra term representing the long range Coulomb interaction. Due to this extra term the model becomes non-integrable and an exact solution is unavailable. However, the non-linear cosine term of this sG model can be expanded provided that δ ex ∼ v/v0 ln W/t < 1, where v is the Fermi velocity, v 0 = e 2 /ǫh, W =hv/a, and a is the smallest length scale in the problem 6 . In this regime a perturbative theory may be applied to calculate excitonic energies. Our work also indicates that a large enhancement of band gap occurs. Our perturbative approach suggests an approximate estimate for when an exciton instability may occur: δ ex > 1 . (We cannot exclude the possibility that the higher order corrections n...

The effect of fluorine neutral/ion-beam irradiation to an n-type GaN surface on the ohmic contact property of a Ti/Al/Au multilayer scheme was investigated. The contact formed after a fluorine neutral-beam treatment showed lower contact resistivity than that formed without the treatment and that formed after a fluorine ion-beam treatment. The irradiation of the fluorine neutral beam is believed to create nitrogen vacancies at the surface region of n-GaN due to the preferential removal of nitrogen, which acts as a donor impurity. In addition, the GaN surface treated by the fluorine neutral beam showed less GaF x formation and smaller surface damage compared to the surface treated by the fluorine ion beam. This resulted in lower ohmic contact resistivity. After annealing at temperatures above 600°C, the contact formed after the fluorine neutral-beam treatment exhibited an excellent linear current-voltage characteristic.Obtaining excellent ohmic contact to GaN-based materials is one of crucial steps in the fabrication of high-performance light emitting diodes ͑LEDs͒ and laser diodes ͑LDs͒. There have been many efforts of ohmic contact formation to n-type GaN-based materials using different metal schemes such as Ti/Al-and V/Al-based metallization. 1-5 In conjunction with the above efforts, surfacetreatment techniques such as wet treatment and plasma treatment have also been proposed as an additional route to realize a good ohmic contact. 6,7 In the case of n-type GaN contact formation, it is well known that the increase in donor concentration at the surface region of the GaN is one of important factors in achieving a good ohmic formation. In the case of the surface treatment, good ohmic contact can be obtained by generating nitrogen vacancy acting as a donor at the surface region of n-type GaN. Jang et al. 8,9 investigated the effects of Cl 2 inductively coupled plasma ͑ICP͒ on the n-type GaN contact properties and found that the Cl 2 plasma treatment improved the ohmic characteristics of metal contacts due to the formation of nitrogen vacancy on the surface of the GaN, resulting in the increase of donor carrier concentration.In the case of plasma treatments, however, if the GaN surface is damaged by ion bombardment during the treatment, ohmic contact properties can be degraded. Ping et al. 7,10 studied the effects of reactive ion etching ͑RIE͒-induced damage on the Schottky and ohmic characteristics of n-GaN contacts. The surface of n-GaN was treated with SiCl 4 and Ar plasmas prior to metallization. They found that the surfaces treated with SiCl 4 plasmas showed improved ohmic contact properties compared to those of the untreated samples for all treatment conditions investigated. The GaN surfaces treated with Ar plasmas showed severely degraded ohmic contact behavior except for the treatment conditions using low self-bias voltages.In this study, the n-GaN surface was treated by fluorine ion and neutral beams and their effects on the n-GaN ohmic contact properties were investigated. Fluorine-based gas was used in th...

The diffusion and surface oxidation rates of Fe deposited on Si and barrier layers of Al/SiO 2 and Al 2 O 3 /SiO 2 have been comparatively studied and correlated with the growth of carbon nanotubes (CNTs). Initially, Fe/samples were subjected to thermal chemical vapour deposition (CVD) at $650 C for $30 min to grow the CNTs. Scanning electron microscopy analysis showed that the height of the CNTs on the Fe/Al 2 O 3 /SiO 2 /Si samples was relatively high ($9.5-11 mm), as compared with the other samples. To investigate this, a few as-prepared samples were thermally annealed at $650 C for $30 min and characterized by dynamic secondary ion mass spectroscopy (D-SIMS) and X-ray photoelectron spectroscopy (XPS). The D-SIMS results showed that the diffusion depth, x Fe , and magnitude of the diffusivity, D Fe , of the Fe atoms are highest for the Fe/Si sample. This is attributed to vacancy-mediated migration, which leads to the formation of unstable, non-stoichiometric Fe-Si and Fe-O-Si phases. However, for the Fe/Al 2 O 3 /SiO 2 /Si samples, the magnitudes of x Fe and D Fe are found to be the lowest, which indicates steric hindrance to Fe by the Al 2 O 3 layers. The XPS analysis revealed that the surface metallic state, after annealing, is almost unaffected for the Fe/Al 2 O 3 /SiO 2 /Si samples, whereas the majority of the Fe precipitate was observed to be oxidized in the case of the other samples.