Vertical Power p-n Diodes Based on Bulk GaN Kizilyalli, Isik C.; Edwards, Andrew P.; Aktas, Ozgur ...
IEEE transactions on electron devices,
02/2015, Letnik:
62, Številka:
2
Journal Article
Recenzirano
There is a great interest in wide-bandgap semiconductor devices and most recently in monolithic GaN structures for power electronics applications. In this paper, vertical p-n diodes fabricated on ...pseudobulk low defect density (10 4 -10 6 cm -2 ) GaN substrates are discussed. Homoepitaxial low-pressure metal organic chemical vapor deposition growth of GaN on its native substrate and being able to control and balance the n-type Si doping with background C impurity has allowed the realization of vertical device architectures with drift layer thicknesses of 6 to 40 μm and net carrier electron concentrations of 4 × 10 15 to 2.5 × 10 16 cm -3 . This parameter range is suitable for applications requiring breakdown voltages (BVs) of 600 V-4 kV with a proper edge termination strategy. Measured devices demonstrate near power device figure of merit, that is, differential specific on-resistance (R sp ) of 2 mΩcm 2 for a BV of 2.6 kV and 2.95 mΩcm 2 for a 3.7-kV device, respectively. The improvement in the substrate quality over the last few years has resulted in the fabrication of diodes with areas as large as 16 mm 2 , with BVs exceeding 700 V and pulsed (100 μs) currents of 400 A. The structures fabricated are utilized to study in detail the temperature dependency of I-V characteristics, impact ionization and avalanche characteristics, and extract (estimate) modeling parameters such as electron mobility in the GaN c-direction (vertical) and hole minority carrier lifetimes. Some insight into device reliability is also provided.
3.7 kV Vertical GaN PN Diodes Kizilyalli, Isik C.; Edwards, Andrew P.; Nie, Hui ...
IEEE electron device letters,
02/2014, Letnik:
35, Številka:
2
Journal Article
Recenzirano
There is a great interest in wide band-gap semiconductor devices for power electronics application. In this letter, vertical GaN p-n diodes fabricated on bulk GaN substrates are discussed. The device ...layers are grown by MOCVD on low defect density (10 4 cm -2 ) bulk GaN substrates. The measured devices show breakdown voltages of 3.7 kV with an area differential specific on-resistance (Rsp) of 2.95 mΩ-cm 2.
Vertical GaN Power Diodes With a Bilayer Edge Termination Dickerson, Jeramy R.; Allerman, Andrew A.; Bryant, Benjamin N. ...
I.E.E.E. transactions on electron devices/IEEE transactions on electron devices,
01/2016, Letnik:
63, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Vertical GaN power diodes with a bilayer edge termination (ET) are demonstrated. The GaN p-n junction is formed on a low threading dislocation defect density (10 4 - 10 5 cm -2 ) GaN substrate, and ...has a 15-μm-thick n-type drift layer with a free carrier concentration of 5 × 10 15 cm -3 . The ET structure is formed by N implantation into the p + -GaN epilayer just outside the p-type contact to create compensating defects. The implant defect profile may be approximated by a bilayer structure consisting of a fully compensated layer near the surface, followed by a 90% compensated (p) layer near the n-type drift region. These devices exhibit avalanche breakdown as high as 2.6 kV at room temperature. Simulations show that the ET created by implantation is an effective way to laterally distribute the electric field over a large area. This increases the voltage at which impact ionization occurs and leads to the observed higher breakdown voltages.
Alta Devices, Inc. has fabricated a thin-film GaAs device on a flexible substrate with an independently-confirmed solar energy conversion efficiency of 27.6%, under AM1.5G solar illumination at 1 sun ...intensity. This represents a new record for single-junction devices under non-concentrated sunlight. This surpasses the previous record, for conversion efficiency of a single-junction device under non-concentrated light, by more than 1%. This is due largely to the high open-circuit voltage (V oc ) of this device. The high V oc results from precise control of the dark current. The fact that this record result has been achieved with a thin-film shows that, for GaAs material systems, the majority of the growth substrate is not needed for device performance. This allows one to consider amortizing the potentially high cost of a GaAs growth substrate by growing a thin-film, lifting it off, and reusing the same substrate multiple times. This technology therefore has the potential to be a novel high-performance, thin-film option for terrestrial photovoltaics.
There is a great interest in monolithic GaN semiconductor devices with high current capability for power electronics. In this letter, large area vertical GaN p-n diodes fabricated on bulk GaN ...substrates are discussed. Diodes with areas as large as 16 mm 2 with breakdown voltages exceeding 700 V and pulsed (100 μs) currents approaching 400 A are reported. This is made possible for the first time in part due to the recent availability of improved quality bulk GaN substrates.
A system is presented that is capable of measuring subnanosecond reverse recovery times of diodes in wide-bandgap materials over a wide range of forward biases (0 - 1 A) and reverse voltages (0 - 10 ...kV). The system utilizes the step recovery technique and comprises a cable pulser based on a silicon (Si) Photoconductive Semiconductor Switch (PCSS) triggered with an Ultrashort Pulse Laser, a pulse charging circuit, a diode biasing circuit, and resistive and capacitive voltage monitors. The PCSS-based cable pulser transmits a 130 ps rise time pulse down a transmission line to a capacitively coupled diode, which acts as the terminating element of the transmission line. The temporal nature of the pulse reflected by the diode provides the reverse recovery characteristics of the diode, measured with a high bandwidth capacitive probe integrated into the cable pulser. This system was used to measure the reverse recovery times (including the creation and charging of the depletion region) for two Avogy gallium nitride diodes; the initial reverse recovery time was found to be 4 ns and varied minimally over reverse biases of 50-100 V and forward current of 1-100 mA.
The purpose of this study was to evaluate and compare the effect of short segment pedicle screw instrumentation and an intermediate screw (SSPI+IS) on the radiological outcome of type A thoracolumbar ...fractures, as judged by the load-sharing classification, percentage canal area reduction and remodelling. We retrospectively evaluated 39 patients who had undergone hyperlordotic SSPI+IS for an AO-Magerl Type-A thoracolumbar fracture. Their mean age was 35.1 (16 to 60) and the mean follow-up was 22.9 months (12 to 36). There were 26 men and 13 women in the study group. In total, 18 patients had a load-sharing classification score of seven and 21 a score of six. All radiographs and CT scans were evaluated for sagittal index, anterior body height compression (%ABC), spinal canal area and encroachment. There were no significant differences between the low and high score groups with respect to age, duration of follow-up, pre-operative sagittal index or pre-operative anterior body height compression (p = 0.217, 0.104, 0.104, and 0.109 respectively). The mean pre-operative sagittal index was 19.6° (12° to 28°) which was corrected to -1.8° (-5° to 3°) post-operatively and 2.4° (0° to 8°) at final follow-up (p = 0.835 for sagittal deformity). No patient needed revision for loss of correction or failure of instrumentation. Hyperlordotic reduction and short segment pedicle screw instrumentation and an intermediate screw is a safe and effective method of treating burst fractures of the thoracolumbar spine. It gives excellent radiological results with a very low rate of failure regardless of whether the fractures have a high or low load-sharing classification score.
Tyrosine kinase inhibitors (TKIs) have dramatically improved chronic myeloid leukemia (CML) prognosis. However, TKIs are associated with dyslipidemia and impaired glucosehomeostasis. ...Triglyceride-to-high-density lipoprotein cholesterol ratio (TG/HDL-C) is proposed to be an indicator of insulin resistance and atherogenic index, but there is no research on TG/HDL-C alterations in patients receiving TKIs for CML. We aimed to evaluate relationships between TKI type/count, clinical characteristics, and laboratory results (particularly TG/HDL-C) in CML patients.
A total of 104 patients with chronic phase CML were enrolled in the study. All patients received initial imatinib therapy at 400 mg daily, the type or dose of TKI was then changed according to treatment response and clinical outcomes. Patients were compared with respect to TG/HDL-C categorization (>2.5 versus <2.5), number of TKIs used, and use of imatinib as the only TKI.
The median TG/HDL-C was 2.82 (1.03-17.33) and this ratio was higher than 2.5 in 59 (56.7%) patients. Patients with high TG/HDL-C had a significantly higher age than patients with low values (P < 0.001). Recipients of more than one TKI had higher EUTOS risk score and white blood cell (WBC) count (P < 0.05). Recipients of imatinib as the only TKI had higher age, low EOTUS risk score, low WBC, and low neutrophil count (all, P < 0.05).
TG/HDL-C values were not associated with the number of different TKIs used or the use of imatinib only in chronic-phase patients with CML. Further large-scale prospective studies are needed to determine whether TG/HDL-C can be used for diagnostic or prognostic purposes in TKI recipients.
The emergence of electrical conversion technologies utilizing silicon carbide and gallium nitride switches and diodes will enable the development of a whole new class of efficient, lightweight, and ...reliable power electronics based on wide band gap semiconductors for photovoltaic (PV) systems. This article presents the results of a study to model the value proposition of these devices when they are used in dc-ac inverters, medium voltage dc-dc converters, as well as solid state breakers and transformers. The conclusions illustrate the beneficial impact on energy generation, operation and maintenance, plant architecture simplification, and associated reduction in capital cost and levelized cost of electricity that these new solid state devices will enable for the future PV system developer.
In this paper, vertical p-n diodes fabricated on pseudobulk gallium nitride (GaN) substrates are discussed. The measured devices demonstrate breakdown voltages of 2600 V with a differential specific ...on-resistance of 2 mΩ cm 2 . This performance places these structures beyond the SiC theoretical limit on the power device figure of merit chart. Contrary to common belief, GaN devices do possess avalanche capability. The temperature coefficient of the breakdown voltage is positive, showing that the breakdown is indeed because of impact ionization and avalanche. This is an important property of the device for operation in inductive switching environments. Critical electric field and mobility parameters for epitaxial GaN layers grown on bulk GaN are extracted from electrical measurements. The reverse recovery time of the vertical GaN p-n diode is not discernible because it is limited by capacitance rather than minority carrier storage, and because of this its switching performance exceeds the highest speed silicon diode.
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