High efficiency ultraviolet light emitting diode with band structure potential fluctuations

• US 10,535,801 B2
• Filed: 04/08/2015
• Issued: 01/14/2020
• Est. Priority Date: 04/30/2010
• Status: Active Grant

• Current Assignee: Trustees of Boston University
• Original Assignee: Boston University
• Inventors: Liao, Yitao, Moustakas, Theodore D.
• Primary Examiner(s): Bell, Lauren R
• Application Number:
  US14/681,327
• Publication Number:
  US 20160211411A1
• Time in Patent Office: 1,742 Days
• CPC Class Codes: H01L 21/0237 Materials
• CPC Class Codes: H01L 21/0242 Crystalline insulating materials
• CPC Class Codes: H01L 21/02458 Nitrides
• CPC Class Codes: H01L 21/02507 Alternating layers, e.g. superlattice
• CPC Class Codes: H01L 21/0254 Nitrides
• CPC Class Codes: H01L 21/02573 Conductivity type
• CPC Class Codes: H01L 21/0259 Microstructure
• CPC Class Codes: H01L 21/02625 using melted materials
• CPC Class Codes: H01L 33/007 comprising nitride compounds
• CPC Class Codes: H01L 33/025 Physical imperfections, e.g. particular concentration or distribution of impurities
• CPC Class Codes: H01L 33/06 within the light emitting region, e.g. quantum confinement structure or tunnel barrier
• CPC Class Codes: H01L 33/14 with a carrier transport control structure, e.g. highly-doped semiconductor layer or current-blocking structure
• CPC Class Codes: H01L 33/32 containing nitrogen

Abstract

A method of growing an AlGaN semiconductor material utilizes an excess of Ga above the stoichiometric amount typically used. The excess Ga results in the formation of band structure potential fluctuations that improve the efficiency of radiative recombination and increase light generation of optoelectronic devices, in particular ultraviolet light emitting diodes, made using the method. Several improvements in UV LED design and performance are also provided for use together with the excess Ga growth method. Devices made with the method can be used for water purification, surface sterilization, communications, and data storage and retrieval.

Claims

1. A device comprising:

an AlGaN quantum well (QW) active layer disposed between an n-type region and a p-type region, wherein the QW active layer emits ultraviolet radiation in a wavelength range between 210 nm and 360 nm and is undoped, the QW active layer having a first AlN mole fraction and a first bandgap;

a QW barrier layer adjacent to the QW active layer, the QW barrier layer being between the QW active layer and the n-type region, the QW barrier layer having a second AlN mole fraction higher than the first AlN mole fraction so as to have a second bandgap higher than the first bandgap of the QW active layer; and

a first layer adjacent to the QW barrier layer and in the n-type region having a third bandgap smaller than the first bandgap of the QW active layer, wherein the first layer is doped with an n-type dopant, the first layer having a third AlN mole fraction that is less than the first AlN mole fraction; and

a second layer in the n-type region and adjacent to the first layer, wherein the second layer has a fourth AlN mole fraction larger than the first AlN mole fraction of the QW active layer, the second AlN mole fraction of the QW barrier layer, and the third AlN mole fraction of the first layer,

the second layer also having a fourth band gap larger than the first bandgap of the QW active layer, the second bandgap of the QW barrier layer, and the third bandgap of the first layer; and

a third layer in the n-type region and adjacent to the second layer, the third layer having a fifth AlN mole fraction lower than the first AlN mole fraction and a fifth bandgap lower than the first bandgap of the QW active layer,

wherein electrons in the first layer tunnel through the QW barrier layer into the QW active layer when the device is energized.

2. The device of claim 1 wherein the QW barrier layer is undoped.

3. The device of claim 1 wherein the QW active layer, the QW barrier layer, the first layer, the second layer, and the third layer are AlGaN.

4. The device of claim 1 wherein the QW active layer has an average aluminum concentration and an average gallium concentration across a total lateral extent of the QW active layer, and a reduced aluminum concentration and a greater gallium concentration as compared to the average aluminum concentration and the average gallium concentration in a localized region, the localized region having a lateral extent that is less than the total lateral extent of the QW active layer.

5. The device of claim 1 wherein the QW active layer is non-faceted.

6. The device of claim 1 wherein the QW active layer emits radiation having a peak wavelength less than 350 nm.