This will count as one of your downloads.
You will have access to both the presentation and article (if available).
In this paper, we analyze the electrical behavior and the deep levels present in nitrogen-implanted gallium oxide Schottky barrier diodes annealed at increasing temperature from 800 °C to 1200 °C. In gallium oxide, nitrogen implantation is used in order to achieve controlled isolation of parts of the final device, and its stability and performance is therefore of high importance.
The high temperature annealing carried out after implantation causes a reduction in the leakage current flowing in the structure, confirming the feasibility of nitrogen implantation as isolation procedure and the annealing of the defects caused by the implantation process.
Repeated current-voltage measurements show the presence of an electron trapping process in the structure. The involved deep levels were investigated by means of isothermal transient spectroscopy tests, and both current and capacitance were used to monitor the trapping level in the devices. A model was developed to explain the full set of collected data on all the annealing temperatures, based on thermionic injection of electrons into an intermediate deep level and on charge injection into the space charge region.
By means of deep level transient spectroscopy experiments we analyzed the various defects present in the samples. Their concentration correlates with the annealing, decreasing at high temperature. All the detected deep levels are consistent with previous reports in the literature, and are attributed to gallium vacancies, native point defects and extrinsic defects.
The market for UV LEDs is experiencing a rapid growth, also driven by the need for effective and efficient disinfection systems. Before UV LEDs can be widely accepted by the market, they need to demonstrate a high reliability, with lifetimes of several thousands of hours. Several physical processes may limit the reliability of UVB and UVC LEDs, resulting in a loss in efficiency during long term operation.
This paper aims at discussing the most relevant processes that can lead to the degradation of UVB and UVC LEDs, with focus on: (i) instability of the electrical properties, which may result in gradual changes in the turn-on voltage of the devices during long-term operation. (ii) The generation of defects within the active region of the devices, with consequent increase in the Shockley-Read-Hall non-radiative recombination rate. Optical spectroscopy is found to be very effective for the identification of deep (midgap) traps during operation of the devices. (iii) trap states near the junction, with consequent impact on trap-assisted-tunneling of the current-voltage characteristics. (iv) the propagation of point defects, especially impurities, and accumulation of charges at heterointerfaces, that can reduce the carrier injection efficiency, thus leading to a decrease in the emitted optical power.
Deep defects have a fundamental role in determining the electro-optical characteristics and in the efficiency of InGaN light-emitting diodes (LEDs). However, modeling their effect on the electrical characteristics of the LED is not straightforward.
In this paper we analyze the impact of the defects on the electrical characteristics of LEDs: we analyze three single-quantum-well (SQW) InGaN/GaN LED wafers, which differ in the density of defects. Through steady-state photocapacitance (SSPC) and light-capacitance-voltage measurements, the energy levels of these deep defects and their concentrations have been estimated.
By means of a simulation campaign, we show that these defects have a fundamental impact on the current voltage characteristic of LEDs, especially in the sub turn-on region. The model adopted takes into consideration trap assisted tunneling as the main mechanism responsible for current leakage in forward bias.
For the first time, we use in simulations the defect parameters (concentration, energy) extracted from SSPC. In this way, we can reproduce with great accuracy the current-voltage characteristics of InGaN LEDs in a wide current range (from pA to mA).
In addition, based on SSPC measurements, we demonstrate that the defect density in the active region scales with the QW thickness. This supports the hypothesis that defects are incorporated in In-containing layers, consistently with recent publications.
The results collected within this paper are explained by considering that stress promotes the diffusion of defects towards the active region of the devices. This mechanism results in a decrease in the SRH recombination lifetime, and in the subsequent increase in threshold current and drop in sub-threshold emission. An increase in the SRH rate next to the quantum dots can also reduce the injection efficiency into the QDs, thus inducing a drop in the slope efficiency of the lasers.
The study showed three main effects: (i) the decrease in the sub-threshold optical power, which shows two different slopes, that we ascribe to the regions where A, Shockley-Read-Hall (SRH) recombination coefficient, and B, radiative coefficient, dominate. (ii) a logarithmic decrease during the stress time of the characteristic temperature T0. (iii) the presence of a parasitic peak, with energy close to the main emission peak. This peak is ascribed to recombination in a second quantum well with slightly different energy, due to the different internal field. The intensity of this excited emission decreases during stress time, possibly due to a change in the injection efficiency.
We have also found an initial increase in the optical power at very low current levels, followed by a decrease with increasing stress time. This behavior is ascribed to an initial annealing, that favors the activation of magnesium, followed by an increment of the density of defects in the material caused by the stress.
View contact details
No SPIE Account? Create one
