We have measured the current-voltage characteristics of two capacitively coupled 1D arrays of small tunnel junctions, where the coupling capacitance is significantly larger than the junction capacitance. We voltage biased only one of the arrays, while the current was measured simultaneously in both arrays. We find that, at low bias voltages, the currents in the two arrays are comparable in magnitude but opposite in direction. The currents are carried by tunneling electron-hole pairs that are bound by the charging energy of the coupling capacitance. [S0031-9007 (97) Several experiments have demonstrated that the Coulomb interaction of the electrons plays an important role in systems of small tunnel junctions. The significant charging energy prohibits electron tunneling below a certain threshold voltage. The charging energy reveals the discrete nature of the electron charge in these systems [1][2][3]. In 1D arrays of small tunnel junctions, the Coulomb interaction leads to transport of charge solitons through the array [4]. The soliton length depends on the ratio between the junction capacitance and the self-capacitance of the islands in between the junctions.Theoretical [5,6] and experimental [7] work on systems of small tunnel junctions has shown that electron transport in the Coulomb blockade regime is possible by electron tunneling through one or more virtual states of higher energy. This macroscopic quantum tunneling (MQT) of the charge or cotunneling is possible even at zero temperature, where charge is transferred through more than one junction in one event. It has been shown [5] that the rate of cotunneling is proportional to ͑R K ͞R͒ M , where R K h͞2e 2 is the resistance quantum, R is the junction tunnel resistance, and M is the number of junctions involved in the cotunneling event. Generally, cotunneling leads to quantum leakage of the current in single-electron tunneling devices. The quantum leakage forms a problem for devices aiming at metrological accuracy of the current [8,9].

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In this paper, the role of a direct plasma hydrogenation treatment and a subsequent air annealing at 450°C in the formation of thermal donors ͑TDs͒ in n-type Czochralski ͑CZ͒ silicon is investigated by means of a combination of capacitance-voltage ͑C-V͒ and deep-level transient spectroscopy ͑DLTS͒. The hydrogenation treatment is found to enhance the introduction rate of TDs at 450°C for shorter annealing times, reaching its maximum acceleration after 5 h and for the longest plasma hydrogenation studied ͑2 h͒. For much longer annealing times, the TD introduction rate becomes independent of the presence of hydrogen in the material. DLTS detects only one donor level having an activation energy, which lowers with increasing doping density of the material, from 0.106 to 0.093 eV. After activation energy correction for the Poole-Frenkel electric-field-enhanced emission, this trap is found to fit well with the conventional singly ionized oxygen thermal donor level. However, from C-V free carrier and DLTS trap concentrations, it is derived that other shallower donors, created by the plasma hydrogenation and 450°C anneal should play an important role in the free carrier concentration increase of the n-CZ silicon.By now, it is a well-accepted fact that hydrogen plays a catalytic role in the formation of thermal donors in Czochralski ͑CZ͒ silicon. 1-4 Hydrogen can be introduced in several ways in the material, among which a hydrogen plasma treatment is of strong interest due to its low cost, high throughput, and low thermal budget. 5 Combining a low-temperature plasma hydrogenation, followed by a relatively short thermal donor anneal at 450°C, it has been demonstrated that p-type starting material can be converted into n-type silicon, and therefore, deep p-n junctions can be obtained in a fast and cheap way. 5,6 The depth of the junction is thereby controlled by the hydrogen in-diffusion profile. 6 So far, most of our studies have focused on p-type CZ starting material. 5,6 In this paper, the impact of the plasma hydrogenation time on the thermal donor ͑TD͒ formation during annealing at 450°C from 30 min up to 50 h in n-type CZ material is investigated. It is shown by capacitance-voltage ͑C-V͒ doping profiles that there is indeed an enhancement of the TD formation rate for annealing times t a450 р 5 h. The maximum effect is observed after a 5 h anneal and increases with increasing plasma hydrogenation time t H , i.e., with the total amount of hydrogen in the material. For longer t a450 , the hydrogen impact diminishes, resulting in a final free electron introduction rate from C-V of about 1.7-1.8 ϫ 10 14 cm Ϫ3 /h for the n-type CZ silicon studied. In order to identify the created donors, deep level transient spectroscopy ͑DLTS͒ was performed on a selected group of samples. The resulting spectra are dominated by a donor level at an energy of 0.093-0.106 eV below the conduction band E C , shifting to lower values for increasing n-type doping density. By taking into account the Poole-Frenkel barrier lowering with increasing el...

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