Source: http://www.google.com/patents/US7994512?ie=ISO-8859-1
Timestamp: 2014-03-07 13:13:40
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Matched Legal Cases: ['Application No. 07254498', 'Application No. 08253301', 'Application No. 200710142217', 'Application No. 10', 'Application No. 2003', 'Application No. 200710142217', 'art 1']

Patent US7994512 - Gallium nitride based diodes with low forward voltage and low reverse ... - Google PatentsSearch Images Maps Play YouTube News Gmail Drive More »Sign inAdvanced Patent SearchPatentsNew Group III based diodes are disclosed having a low on state voltage (Vf) and structures to keep reverse current (Irev) relatively low. One embodiment of the invention is Schottky barrier diode made from the GaN material system in which the Fermi level (or surface potential) of is not pinned. The barrier...http://www.google.com/patents/US7994512?utm_source=gb-gplus-sharePatent US7994512 - Gallium nitride based diodes with low forward voltage and low reverse current operationAdvanced Patent SearchPublication numberUS7994512 B2Publication typeGrantApplication numberUS 11/173,035Publication dateAug 9, 2011Filing dateJun 30, 2005Priority dateJul 23, 2001Also published asCA2454310A1, CN1555581A, CN100373634C, CN101127368A, CN101127368B, EP1410445A2, EP1410445B1, EP2315256A2, EP2315256A3, US6949774, US7476956, US20030015708, US20030062525, US20040080010, US20050242366, WO2003026021A2, WO2003026021A3Publication number11173035, 173035, US 7994512 B2, US 7994512B2, US-B2-7994512, US7994512 B2, US7994512B2InventorsPrimit Parikh, Umesh MishraOriginal AssigneeCree, Inc.Export CitationBiBTeX, EndNote, RefManPatent Citations (59), Non-Patent Citations (87), Classifications (18) External Links: USPTO, USPTO Assignment, EspacenetGallium nitride based diodes with low forward voltage and low reverse current operationUS 7994512 B2Abstract New Group III based diodes are disclosed having a low on state voltage (Vf) and structures to keep reverse current (Irev) relatively low. One embodiment of the invention is Schottky barrier diode made from the GaN material system in which the Fermi level (or surface potential) of is not pinned. The barrier potential at the metal-to-semiconductor junction varies depending on the type of metal used and using particular metals lowers the diode's Schottky barrier potential and results in a Vf in the range of 0.1-0.3V. In another embodiment a trench structure is formed on the Schottky diodes semiconductor material to reduce reverse leakage current. and comprises a number of parallel, equally spaced trenches with mesa regions between adjacent trenches. A third embodiment of the invention provides a GaN tunnel diode with a low Vf resulting from the tunneling of electrons through the barrier potential, instead of over it. This embodiment can also have a trench structure to reduce reverse leakage current.
Other hybrid structures have been reported with a Vf of approximately 0.25V (with a barrier height of 0.58V) with operating current density of 100 A/cm2. [M. Mehrotra, B. J. Baliga, �The Trench MOS Barrier Shottky (TMBS) Rectifier�, International Electron Device Meeting, 1993]. One such design is the junction barrier controlled Schottky rectifier having a pn-junction used to tailor the electric fields to minimize reverse leakage. Another device is the trench MOS barrier rectifier in which a trench and a MOS barrier action are used to tailor the electrical field profiles. One disadvantage of this device is the introduction of a capacitance by the pn-junction. Also, pn-junctions are somewhat difficult to fabricate in Group III nitride based devices.
The Gallium nitride (GaN) material system has been used in opto-electronic devices such as high efficiency blue and green LEDs and lasers, and electronic devices such as high power microwave transistors. GaN has a 3.4 eV wide direct bandgap, high electron velocity (2�107 cm/s), high breakdown fields (2�106 V/cm) and the availability of heterostructures.
SUMMARY OF THE INVENTION The present invention provides new Group III nitride based diodes having a low Vf. Embodiments of the new diode also include structures to keep reverse current (Irev) relatively low.
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a GaN Schottky diode embodiment of the invention;
DETAILED DESCRIPTION OF THE INVENTION FIG. 1 shows a Schottky diode 10 constructed in accordance with the present invention having a reduced metal-to-semiconductor barrier potential. The new diode is formed of the Group III nitride based material system or other material systems where the Fermi level is not pinned at its surface states. Group III nitrides refer to those semiconductor compounds formed between nitrogen and the elements in Group III of the periodic table, usually aluminum (Al), gallium (Ga), and indium (In). The term also refers to ternary and tertiary compounds such as AlGaN and AlInGaN. The preferred materials for the new diode are GaN and AlGaN.
The new diode 10 has an n+ GaN layer 12 on a substrate 11 and an n− layer of GaN 13 on the n+ GaN layer 12, opposite the substrate 11. The n+ layer 12 is highly doped with impurities to a concentration of at least 1018 per centimeter cubed (cm3), with the preferable concentration being 5 to 10 times this amount. The n− layer 13 has a lower doping concentration but is still n− type and it preferably has an impurity concentration in the range of 5�1014 to 5�1017 per cm3. The n-layer 13 is preferably 0.5-1 micron thick and the n+ layer 12 is 0.1 to 1.5 microns thick, although other thicknesses will also work.
Barrier Height=work function−the semiconductor's electron affinity FIG. 2 is a graph 20 showing the metal work function 21 for various metal surfaces in a vacuum, verses the particular metal's atomic number 22. The metal should be chosen to provide a low Schottky barrier potential and low Vf, but high enough so that the reverse current remains low. For example, if a metal were chosen having a work function equal to the semiconductor's electron affinity, the barrier potential approaches zero. This results in a Vf that approaches zero and also increases the diode's reverse current such that the diode becomes ohmic in nature and provides no rectification.
This redistribution occurs due to the coupling of the charge in the mesa 49 with the Schottky metal 48 on the top surface and with the metal on the trench sidewalls 46 a and bottom surface 46 b. The depletion then extends from both the top surface (as in a conventional Schottky rectifier) and the trench sidewalls 46 a, depleting the conduction area from the sidewalls. The sidewall depletion reduces the electrical field under the Schottky metal layer 48 and can also be thought of as �pinching off� the reverse leakage current. The trench structure 45 keeps the reverse leakage current relatively low, even with a low barrier potentials and a low Vf.
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