Contact Diode Research Articles

Barrier inhomogeneities and electrical characteristics of Ni/Ti bilayer Schottky contacts on 4H–SiC after high temperature treatments

AbstractThe analysis of “nonideal” behaviour in current–voltage characteristics of fabricated Schottky diodes on 4H–SiC is carried out. An accurate theoretical modelling of the effect of the presence of inhomogeneities on the electron transport across the metal‐semiconductor interface is applied. This model trends to explain a large series of abnormal experimental results obtained on “real” Schottky diodes. Our results clearly demonstrate that the electron transport at the metal–semiconductor interface is significantly affected by low barrier regions. It is suggested that the commonly observed larger‐than‐unity ideality factors, underestimation of the Richardson constant and Schottky Barrier Height correlation with ideality factor can be attributed to an effective area involved in the current transport which may be significantly lower than the geometric area of the diode contact. It is also proved by comparing different types of Schottky diodes that in order to properly characterise the interface uniformity, not only the absolute value of the ideality factor is important but also its temperature dependence and its correlation with barrier height have to be taken into account. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Improvement of the luminous intensity of light-emitting diodes by using highly transparent Ag-indium tin oxide p-type ohmic contacts

We have investigated Ag-indium tin oxide (ITO) scheme for obtaining high-quality p-type ohmic contacts for GaN-based light-emitting diodes (LEDs). The Ag(1 nm)-ITO(200 nm) contacts exhibit greatly improved electrical characteristics when annealed at temperatures in the range 400/spl deg/C-600/spl deg/C for 1 min in air, yielding specific contact resistances of /spl sim/10/sup -4/ /spl Omega//spl middot/cm/sup 2/. In addition, the contacts give transmittance of about 96% at 460 nm, which is far better than that of the conventionally used oxidized Ni-Au contacts. It is shown that the luminous intensity of blue LEDs fabricated with the Ag-ITO contacts is about three times higher than that of LEDs with oxidized Ni-Au contacts. This result strongly indicates that the Ag-ITO scheme can serve as a highly promising p-type ohmic contact for the realization of high brightness near ultraviolet LEDs.

Cu -doped indium oxide∕Ag ohmic contacts for high-power flip-chip light-emitting diodes

We have investigated Cu-doped In2O3(CIO)(3nm)∕Ag(250nm) schemes for forming high-quality ohmic contacts to p-type GaN for high-power flip-chip light-emitting diodes (FCLEDs). It is shown that the CIO∕Ag contacts produce specific contact resistance of 1.28×10−5Ωcm2 and reflectance of about 90% at a wavelength of 460nm when annealed at 530°C for 1min in air ambient. It is also shown that unlike single Ag contacts, the CIO∕Ag contacts are fairly stable without surface and interface degradation although annealed at 530°C for 1min in air ambient. In addition, blue multiquantum-well InGaN∕GaN LEDs fabricated with the annealed CIO∕Ag contact layers give forward-bias voltages of around 3.0V at an injection current of 20mA. The results strongly indicate that the CIO∕Ag scheme can be a highly promising p-type contact for high-power GaN-based FCLEDs for solid-state lighting application.

Back contact and reach-through diode effects in thin-film photovoltaics

The physics of back contact effects in photovoltaic devices is revisited. We show that the back contact Schottky barrier can act in either back-diode or reach-through diode regimes. This understanding predicts that rare local spots with low back barrier hole transparency and/or weak main junctions can shunt the photocurrent thus decreasing the measured open-circuit voltage and device efficiency. We derive several more specific predictions of our model and verify them experimentally for the case of thin-film CdTe photovoltaics. Our concept has practical implications: a simple recipe leading to an efficient (13%) copper-free CdTe solar cell.

Contact diode laser tonsillectomy in children

To compare contact diode laser (CDL) tonsillectomy to monopolar cautery (MPC) with regard to pain and other morbidity during recovery. Single-blind, randomized trial in a tertiary-care pediatric hospital. Tonsillectomy was performed by CDL in 30 children and by MPC in 28. Parents completed a daily questionnaire for 10 days after surgery. There was significantly less pain in the CDL group than in the MPC group. The CDL group also required much less medication, and was much less likely to experience multiple awakenings (P < 0.001 for all comparisons). Recovery after CDL tonsillectomy was associated with much less pain and discomfort than after MPC surgery. Postoperative pain is a major concern for surgeons, patients, and their parents. The long recovery period also has costs in school days missed for the child and work missed for the parents. CDL tonsillectomy may greatly mitigate these burdens.

Surface morphologies of excimer-laser annealed BF 2+ implanted Si diodes

Laser-induced surface roughness and damage formation in ultra-shallow n +–p and p +–n junctions, formed by low energy (5 keV) As + and BF 2 + implantations in Si, respectively, with a dose of 1 × 10 15 cm −2 have been investigated by atomic force microscopy (AFM) and Positron Annihilation Doppler Broadening (PADB) technique. The Si surface roughness is found to increase with laser energy density, and reaches a value of 3.5 nm after excimer-laser annealing (ELA) at 1100 mJ/cm 2. However, anomalous behavior is witnessed for BF 2 +-implanted Si sample at 800 mJ/cm 2, at which energy very high surface protrusions up to 9 nm high are observed. By PADB this behavior is correlated to extensive deep microcavity formation in the Si whereby the volatile F 2 fraction can accumulate and evaporate/out-diffuse, leading to Si surface roughening. The consequences for the diode characteristics and contact resistivity are examined.

Self-aligned silicides for Ohmic contacts in complementary metal–oxide–semiconductor technology: TiSi2, CoSi2, and NiSi

Metal silicides continue to play an indispensable role during the remarkable development of microelectronics. Along with several other technological innovations, the implementation of the self-aligned silicide technology paved the way for a rapid and successful miniaturization of device dimensions for metal–oxide–semiconductor field-effect transistors (MOSFETs) in pace with the Moore’s law. The use of silicides has also evolved from creating reliable contacts for diodes, to generating high-conductivity current paths for local wiring, and lately to forming low-resistivity electrical contacts for MOSFETs. With respect to the choice of silicides for complementary metal–oxide–semiconductor (CMOS) technology, a convergence has become clear with the self-alignment technology using only a limited number of silicides, namely TiSi2, CoSi2, and NiSi. The present work discusses the advantages and limitations of TiSi2, CoSi2, and NiSi using the development trend of CMOS technology as a measure. Specifically, the reactive diffusion and phase formation of these silicides in the three terminals of a MOSFET, i.e., gate, source, and drain, are analyzed. This work ends with a brief discussion about future trends of metal silicides in micro/nanoelectronics with reference to potential material aspects and device structures outlined in the International Technology Roadmap for Semiconductors.

Contact diode laser myringotomy and mitomycin C in children

Objective To investigate the use of contact diode laser myringotomy (C-LAM), combined with topical mitomycin C, as an alternative method for prolonged middle ear ventilation in children with otitis media with effusion. Study design and setting Prospective study at a tertiary care pediatric institution. Methods Fifteen children enrolled in the study. Mitomycin C was applied to the intact tympanic membrane in the right ears, whereas saline on the left side was used for controls. C-LAM was then performed in all ears. Outcome measures included healing rate and scarring, ear infection, and long-term audiometric follow-up. Results There was no significant difference in median healing rate. In each group, the median was between the third and fourth month. Normal hearing thresholds were obtained in all children at 2-year follow-up. Conclusion C-LAM proved to be an effective method for medium-term ventilation, but topical mitomycin C before C-LAM did not prolong patency rate in our patients. No significant complication was encountered at 2-year follow-up.

Low-resistance and highly-reflective Zn–Ni solid solution/Ag ohmic contacts for flip-chip light-emitting diodes

We have investigated a Zn–Ni solid solution/Ag scheme for use in producing high-quality ohmic contacts for flip-chip light-emitting diodes (LEDs). The as-deposited contact shows nonlinear I–V characteristics. However, oxidizing the contacts at temperatures of 350–550 °C for 1 min in air ambient results in linear I–V behaviors, yielding specific contact resistances of 10−4–10−5 Ω cm2. In addition, LEDs are fabricated with the oxidized Zn–Ni solid solution/Ag contacts and Ag single contacts. The typical I–V characteristics of the LEDs with the annealed Zn–Ni solid solution (2.5 nm)/Ag (200 nm) p-type contact layers reveal a forward-bias voltage of 3.25 V at an injection current of 20 mA, which is much better than that of the LEDs with the Ag (200 nm) contact layers.

Omnidirectional reflective contacts for light-emitting diodes

An electrically conductive omnidirectional reflector (ODR) is demonstrated in an AlGaInP light-emitting diode (LED). The ODR serves as p-type contact and comprises the semiconductor, a metal layer and an intermediate low-refractive index dielectric layer. The dielectric layer is perforated by an array of AuZn microcontacts thus enabling electrical conductivity. It is shown that the ODR significantly increases light extraction from an AlGaInP LED as compared to a reference LED employing a distributed Bragg reflector (DBR). External quantum efficiencies of 18% and 11% are obtained for the ODR- and the DBR-LED, respectively.

Iris Retraction and Retroflexion After Transscleral Contact Diode Laser Photocoagulation

A 9-year-old girl with refractory glaucoma with an anterior chamber intraocular lens underwent transscleral contact diode laser cyclophotocoagulation. Slit-lamp examination and ultrasound biomicroscopy revealed iris retraction and retroflexion at 2 weeks of follow-up. The probable cause of this complication is discussed.

Schottky diode back contacts for high frequency capacitance studies on semiconductors

A technique using large-area Schottky diode back contacts has been developed to enable high frequency capacitance studies to be carried out on semiconductors without the need to fabricate high quality ohmic back contacts. This technique will find application for very high resistivity materials or for the characterization of novel semiconductors when a method of producing good ohmic contacts has not been established. In this method a back contact much larger in area than the front contact diode under test is used. It is then found that accurate capacitance–voltage measurements can be made of the ionized doping density and, provided the back contact has sufficient leakage, the built-in potential can also be measured. Such specimens may also be used for characterization using the deep level transient spectroscopy (DLTS) technique and this is demonstrated by obtaining DLTS spectra from very high resistivity silicon specimens containing oxygen precipitates and comparing these to similar spectra obtained from more highly doped material.

Contact diode laser myringotomy with mitomycin C

Contact diode laser myringotomy with mitomycin C

Impact of critical processes on HgCdTe diode performance and yield

HgCdTe detector performance and yield are strongly dependant on CdZnTe substrate and HgCdTe epilayer properties, and on key device processes, especially for 8-12 μm application. Due to the correlation and optimization between these figures and diode performance, AIM has developed a mature HgCdTe technology for superior detector performance and high production rate. To meet high yield and performance for long wavelength (LW) HgCdTe diodes, dislocation densities of < × 10 5 cm -2 both in substrate and epilayer have to be ensured. By a unique AIM substrate growth process, dislocation densities of 2 x 10 4 -9 x 10 4 cm -2 are achieved for all substrates and epilayers (100% yield). The etch pit density (EPD) on (111) epilayers is revealed by an AIM proprietary etching procedure. One critical effect is the dislocations in the diode area, which can originate from the substrate and epilayer growth and the subsequent device processes, respectively. Our studies have shown that device processes can cause additional dislocations in the diode area. Diode yield was clearly improved by a combination of wet and dry etching for diode contact etching.

GaSb and InAs: New Materials for Metal-Semiconductor Point-Contact Diodes

Metal-semiconductor point contact diodes have proved to be good detectors and mixers for radiation from the far-infrared to visible. Until now GaAs, InSb and InP are the most studied and used semiconductor materials for these devices. In this work we present the performance in the visible and infrared region for metal-semiconductor point-contact diodes with GaSb or InAs as the semiconductor layers. These two new materials have shown good characteristics.

Pupillary distortion and staphyloma following transscleral contact diode laser cyclophotocoagulation; a clinicopathological study of three patients

Pupillary distortion and staphyloma following transscleral contact diode laser cyclophotocoagulation; a clinicopathological study of three patients

Influence of total energy delivery on success rate after contact diode laser transscleral cyclophotocoagulation: a retrospective case review and meta-analysis.

To evaluate the effect of a single treatment of contact diode laser transscleral cyclophotocoagulation (TSCP) on intraocular pressure (IOP) in patients with refractory glaucoma and perform a historical meta-analysis of the relationship between successful IOP control and various laser parameters. Clinical data for 47 eyes of 43 patients who underwent a single session of contact diode laser TSCP (power of 2000 mW, exposure time of 2 seconds and 25.6 average applications) for refractory glaucoma at Pasco Eye Institute between 1996 and 2001 were reviewed. Baseline IOP was compared with the postoperative IOP at 1 month, 3 to 6 months, and 1 year. Snellen visual acuity and the number of glaucoma medications being used 3 to 6 months postoperatively were compared with baseline. Complications were also evaluated. The relationship between successful IOP control and various laser parameters (energy applied per eye, energy per laser application, power, exposure time and number of laser applications) was examined using the results of this study and previous investigations. The mean +/- standard deviation (SD) baseline IOP was 29.4 +/- 10.9 mm Hg. Diode laser TSCP decreased average IOP to 15.7 +/- 12.0 mm Hg at 1 month, 16.3 +/- 4.2 mm Hg at 3 to 6 months, and 16.2 +/- 4.8 mm Hg at 1 year, postoperatively. This represents an IOP reduction of approximately 45%. The percentage of patients maintaining a postoperative IOP of <21 mm Hg was 95.7% at 1 month, 92.1% at 3 to 6 months, and 94.4% at 1 year after TSCP. At the 3 to 6 month postoperative visit, the average +/- SD change in Snellen visual acuity (-0.5 +/- 1.1 lines) and the number of glaucoma medications used did not differ significantly from baseline. Combined analysis of the results of this study and previous studies reveals a linear, direct correlation (r = 0.91) between the percentage of patients achieving a successful outcome (defined as a final IOP < 21 or 22 mm Hg) and the total energy delivered to the ciliary body during the treatment session. Diode laser TSCP is a safe and highly effective method for lowering IOP in patients with uncontrolled glaucoma. Higher total energy levels in a given treatment session appear to be associated with increased success as defined by the percentage of patients achieving an IOP < 21 or 22 mm Hg, without an increased risk of additional complications or vision loss.

X-Ray Absorption Fine Structure Measurement Using a Scanning Capacitance Microscope: Trial for Selective Observation of Trap Centers in the ∼nm Region

For site-selective analysis of trap centers in a single nano-structure of a semiconductor, a new X-ray absorption spectroscopy technique using scanning probe detection of capacitance (scanning capacitance microscope-X-ray absorption fine structure; SCM-XAFS method) is proposed. Since capacitance is sensitive to localized electrons, X-ray induced photoionization of a trap center can be detected by capacitance change of the diode structure. The X-ray photon energy dependence of the capacitance involved in a point contact diode of a GaAs sample and Au-coated Si tip of SCM indicates XAFS spectra of the trap centers in the local region. Several resonant X-ray absorption peaks with different sample bias voltage dependences are found. The correspondence of the Fermi level to the specific trap level enhances the SCM-XAFS signal from the trap center, indicating that the site-selective observation of the trap center can be realized by bias control.

High-Energy Proton Irradiation of MgO/GaN Metal Oxide Semiconductor Diodes

MgO/GaN metal oxide semiconductor diodes were irradiated with 40 MeV protons at a fluence of 5 X 10 9 cm - 2 , simulating long-term (10 yr) exposure in space-born applications. The result of the proton irradiation was a decrease in device capacitance, consistent with the creation of deep electron traps that reduce the effective channel doping and also a decrease in breakdown field from ∼10 6 V cm - 1 in control devices to 0.76 X 10 6 V cm - 1 in devices irradiated with the gate metal in place. The capacitance of the device irradiated with the contacts in place recovers to the same value as the contact diodes. The D i t values are decreased by the H 2 anneal in both the unirradiated and irradiated devices.

一期的完全閉鎖するレーザーメスを使った痔ろう根治手術について

一期的完全閉鎖するレーザーメスを使った痔ろう根治手術について