Hoon Young Cho

Electric‐field‐enhanced dissociation of the hydrogen‐Si donor complex in GaAs

The passivation and dissociation process of the hydrogen‐Si donor complex in plasma‐hydrogenated GaAs was presented. The temperature dependent values of dissociation frequencies νd which the first‐order kinetics permit, satisfy the relation νd=5.7×1013 exp(−1.79±0.05 eV/kT) s−1 for the no‐biased anneals. During electric‐field‐enhanced anneal experiments, we confirm that no in‐diffusion from the passivated region to the bulk is observed in the temperature ranges below 150 °C, and that there is a dissociation frequency region independent of the annealing temperature. Finally, from the electric field annealing experiment on the passivated donor in n‐type GaAs, it is suggested that the hydrogen atom in Si‐doped GaAs exposed to the plasma hydrogen is negatively charged with the gain of free electrons and passivates the Si donor, and also that the hydrogen atom or the electron of the hydrogen‐Si donor complex can be easily released by the electric field.

Effects of leakage current on isothermal capacitance transient spectroscopy signals for midgap levels in GaAs

The leakage current effects for the midgap levels in the electron‐beam‐metallized (EBM) Al/GaAs junction were studied by isothermal capacitance transient spectroscopy. In this junction, a new electron deep level which might be due to the surface defects induced during the EBM process was detected. The observed thermal emission time constants of the new deep level and the EL2 level (Ec −0.81 eV) in EBM‐Al/GaAs were increased during the low‐temperature annealing up to 355 °C, while the leakage current density in this junction was decreased down about 4×10−7 A/cm2. We represent that these behaviors of the midgap levels could be well explained by the effect of the leakage current in the Al/GaAs Schottky junction.

Deep levels in undoped bulk InP after rapid thermal annealing

Deep levels in rapid thermal annealed InP in metal‐insulator‐semiconductor (MIS) structures have been studied using deep level transient spectroscopy. Two different insulating layers used in forming MIS structures, a silicon nitride layer and an oxide layer, were fabricated by plasma enhanced chemical vapor deposition and concentrated nitric acid, respectively. In the samples annealed at temperatures between 700 and 900 °C for 10 s, two deep levels having apparent energy depths of 0.43 and 0.35 eV below the conduction band were newly generated. Then, it is considered that they are the defects related with phosphorus vacancy and its complex. Other deep levels observed between 0.55 and 0.79 eV below the conduction band were related with insulating layers. We show an evidence that they might be interface states in the junction of InP and insulator.

Metastable behavior of deep levels in hydrogenated GaAs

New metastable behavior of deep levels is found in hydrogenated GaAs doped with Si. A deep level at 0.60 eV below the conduction‐band minimum (Ec) is generated during hydrogenation and shows metastable for the Ec − 0.42 eV trap. From the defect transformations observed in biased anneals, these defects are found to be metastable defects associated with hydrogen atoms. Especially, the 400 K biased‐anneal experiments indicate that an Ec−0.33 eV trap could be an electric field induced defect, transformed from other intrinsic defects. The Ec − 0.60 eV trap in hydrogenated GaAs could be a hydrogen complex associated with Ec − 0.42 eV trap and the hydrogen atom plays an important role in a metastability of deep level defects in GaAs.

Positively charged states of a hydrogen atom in p‐type InP

It has been demonstrated that atomic hydrogen drifts as a charged state in p‐type InP and the presence of a high‐electric field strongly affects the dissociation of the hydrogen‐acceptor complex. During reverse‐bias anneal experiments on the n+‐p diode, it is confirmed that a charged hydrogen is accelerated out the high‐field region below the breakdown voltage. The dissociation frequencies dependent on the applied bias voltage increase from 5.6×10−6 to 2.3×10−5 s−1 at 150 °C as the bias voltage is increased from 3 to 9 V. The dissociation energies calculated from the first‐order kinetics are in the ranges of 1.58–1.40 eV, at 3–7 V annealing. It is proposed that atomic hydrogen in Zn‐doped p‐type InP exposed to the plasma hydrogen could be positively charged and strongly passivates the charged Zn acceptor, and also the hydrogen of the hydrogen‐Zn acceptor complex can be released with the help of minority carriers or/and the loss of the charged hydrogen atom by the electric field.

Deep levels in Si-implanted and rapid thermal annealed semi-insulating GaAs

Deep levels have been investigated in Si-implanted and rapid-thermal-annealed semiinsulating GaAs:Cr, which was grown by a horizontal Bridgman method. Samples were implanted with a Si-dose of (1 - 5) x 1012 ions cm-2 with 100 keV energy, and treated by a two-step rapid thermal annealing process at 900 and 800° C. After these processes, three electron deep levels at 0.81, 0.53 and 0.62 eV below the conduction band and three hole deep levels at 0.89, 0.64 and 0.42 eV above the valence band were observed. The new deep levels Ec- 0.53 eV, Ec- 0.62 eV, andEv + 0.64 eV in fact, dominate the implantation and/or the thermally damaged region, but are not found in the bulk. These results indicate that high-density deep levels may be induced near or within the implanted region by rapid heating and cooling, and that these defects may effect carrier activation.

Deep levels in GaAs grown on Si during rapid thermal annealing

Deep levels in GaAs on Si substrates grown by metalorganic chemical vapor deposition (MOCVD) were studied during infrared rapid thermal annealing. For GaAs layers on Si after annealing at 850 °C for 20 s, three electron deep levels at 0.36, 0.27, and 0.20 eV below the conduction band were created as the dominant deep levels. Especially, the 0.36 eV level was found to increase up to 40% of the donor concentration as the thickness of Si substrates increased. These results indicate that rapid thermal annealing of GaAs on Si may induce high‐density deep levels due to a biaxial tensile stress caused by the difference in thermal expansion coefficients.

Room‐temperature hydrogenation effect on Si‐ and Be‐ion‐implanted GaAs

Hydrogenation effects on Si‐ and Be‐ion‐implanted GaAs exposed to the hydrogen plasma were investigated. In the sample hydrogenated for 60 min at room temperature, electron mobilities were increased about 21% at 300 K and 1400 cm2/V s at 150 K, showing a little change of the activated Si donor profile. Also, by using deep‐level transient spectroscopy and optical deep‐level transient spectroscopy, it was observed that the electron and hole traps at Ec−0.62‐ and Ev+0.68‐eV levels, which have been reported as defects due to the implanted damage, were efficiently decreased during the room‐temperature hydrogenation. This effect persists during the anneal at 400 °C during 5 min in an argon ambient.

Deep electron traps in GaAs layers grown on (100)Si substrates by metalorganic chemical vapor deposition

Deep electron traps in GaAs layers grown on (100) 3 °‐off Si substrates by metalorganic chemical vapor deposition were investigated by deep‐level transient spectroscopy and a computer simulation method. The four electron traps with the activation energies of 0.81, 0.68, 0.57, and 0.53 eV below the conduction band were measured in GaAs epilayers on Si substrates, whereas only the EL2 level (Ec−0.81 eV) was detected in GaAs on a GaAs substrate. From the dependencies of concentration on the thickness of GaAs epilayer and Si substrate, it was assumed that the Ec−0.57 eV trap might be a Si‐dislocation complex defect. The Ec−0.68 eV trap showed a similar behavior to that of the deep trap created in the plastically deformed bulk GaAs, and then its origin was supposed to be a defect induced by a stress due to the differences of thermal expansion coefficient and lattice parameter between Si and GaAs.

Deep levels in Si- and Be-coimplanted GaAs

Deep levels and electrical properties in Si‐ and Be‐coimplanted semi‐insulating GaAs, grown by liquid‐encapsulated Czochralski methods, were investigated. The Si implantation with a dose of 8×1012 ions cm−2 and energy of 65 keV was performed into GaAs already implanted with a Be dose of 2×1012 cm−2 and 90 keV for the purpose of an abrupt implant profile in a deeper region. During the Be coimplantation, an electron deep level at 0.62 eV below the conduction band and a hole deep level at 0.68 eV above the valence band were newly observed. In the Be‐implanted region of ion‐implanted GaAs, the deep levels Ec − 0.62 eV and Ev + 0.68 eV dominate, but are not found in the bulk. From this work, it is suggested that the Ec − 0.62 eV trap could be the defect due to the implantation damage and that the Ev + 0.68 eV trap could be the Be complex related to a Si dose during the implantation.