Pure green light emitting diodes and method of manufacturing the same

• US 4,965,644 A
• Filed: 11/12/1985
• Issued: 10/23/1990
• Est. Priority Date: 07/28/1982
• Status: Expired due to Term

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Iwasa, Hitoo, Kawabata, Toshiharu, Koike, Susumu, Matsuda, Toshio
• Primary Examiner(s): Sikes, William L.
• Assistant Examiner(s): Wise, Robert E.
• Application Number:
  US06/797,756
• Time in Patent Office: 1,806 Days
• Field of Search: 357/17, 357/63, 357/30
• US Class Current: 257/88
• CPC Class Codes: H01L 33/0062 for devices with an active region comprising only III-V compounds
• CPC Class Codes: H01L 33/30 containing only elements of Group III and Group V of the Periodic Table

Abstract

Pure-green light emitting diodes include an n-type GaP layer formed on an n-type GaP substrate and a p-type GaP layer formed by using a liquid phase epitaxial method, the average donor concentration of the p-type GaP layer being less than or equal to 5×10¹⁶ cm^-3. Liquid phase crystal growth of the above p-type GaP layer is realized by applying a method of keeping the melt used for the liquid phase crystal growth of the n-type GaP layer at a constant temperature and the ambient atmosphere at a reduced pressure for a prescribed period of time thereby to volatilize donor impurities from the melt and to compensate the donor impurities. Pure-green light emitting diodes easily distinguishable from yellow-green and having high brightness can be manufactured by applying the over-compensation method which is suitable for mass production.

Claims

1. A pure green light emitting diode, comprising:

an n-type gallium phosphide substrate;

an n-type gallium phosphide epitaxial layer, said n-type layer being formed overlying said substrate as a liquid phase epitaxial layer; and

a p-type gallium phosphide epitaxial layer grown by a liquid phase epitaxial process on said n-type layer, said p-type layer containing donor impurities in an average donor concentration less than or equal to 5×

10¹⁶ cm^-3, such that brightness of said pure green light emitting diode attains a predetermined high brightness value with an emission peak wavelength of 555 nm.

2. A method for manufacturing a pure-green light emitting diode, comprising the steps of:

preparing an n-type gallium phosphide substrate;

bringing a melt for epitaxial growth containing donor impurities into contact with said substrate and decreasing a temperature of said melt at a predetermined cooling rate to cause an n-type gallium phosphide layer to grown epitaxially in liquid phase on said substrate, said donor impurities being sulfur;

maintaining the temperature of said melt at a temperature at which growth of said n-type gallium phosphide layer becomes complete and maintaining an ambient atmosphere at a reduced pressure for a predetermined period of time thereby to volatilize donor impurities from said melt; and

terminating maintenance of said ambient atmosphere at said reduced pressure and decreasing the temperature of said melt at a predetermined cooling rate while adding receptor impurities to said melt in vapor phase thereby to form a p-type gallium phosphide epitaxial layer having an average donor concentration of less than or equal to 5×

10¹⁶ cm^-3 on said n-type gallium phosphide layer and thereby to form a pn junction, said pure-green average donor concentration of 5×

10¹⁶ cm^-3 being selected such that brightness of said light emitting diode attains a predetermined high brightness value with an emission peak wavelength of 555 nm, said acceptor impurities being zinc.

3. A method for manufacturing a pure green light emitting diode, comprising the steps of:

preparing an n-type gallium phosphide substrate;

bringing a melt for epitaxial growth containing donor impurities into contact with said substrate and decreasing a temperature of said melt at a predetermined cooling rate to cause an n-type gallium phosphide layer to grow epitaxially in liquid phase on said substrate;

maintaining the temperature of said melt at a temperature at which growth of said n-type gallium phosphide layer becomes complete and maintaining an ambient atmosphere at a reduced pressure for a predetermined period of time thereby to volatilize donor impurities from said melt; and

terminating maintenance of said ambient atmosphere at said reduced pressure and decreasing the temperature of said melt at a predetermined cooling rate while adding acceptor impurities to said melt in vapor phase thereby to form a p-type gallium phosphide epitaxial layer having an average donor concentration of less than or equal to 5×

10¹⁶ cm^-3 on said n-type gallium phosphide layer and thereby to form a pn junction, said average donor concentration of 5×

10¹⁶ cm^-3 being selected such that brightness of said light emitting diode attains a predetermined high brightness value with an emission peak wavelength of 555 nm.

4. A method for manufacturing a pure-green light emitting diode according to claim 3, wherein said predetermined period during which said ambient atmosphere is maintained at said reduced pressure is longer than or equal to 3 hours.

5. A method for manufacturing a pure-green light emitting diode according to claim 3, wherein said predetermined cooling rate of said melt is 1°

C./min.