Fishing – trapping – and vermin destroying
Patent
1989-03-08
1990-05-01
Hearn, Brian E.
Fishing, trapping, and vermin destroying
437117, 437905, 437974, 148DIG99, 148DIG108, 148DIG135, H01L 2120
Patent
active
049218174
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Technical Field
This invention relates to a method of epitaxially growing a substrate for a high-intensity LED. More particularly, the invention relates to a method of epitaxial growth necessary for forming a stable electrode having little contact resistance and exhibiting ohmic properties for the purpose of manufacturing a high-intensity LED chip.
2. Background Art
In order to epitaxially grow a substrate for, say, a red-light emitting high-intensity LED in the prior art, first a layer of Zn-doped Al.sub.0.75 Ga.sub.0.25 As (p-type) is formed as a p-type cladding layer to a thickness of 200 microns on a p-type GaAs substrate [(100) surface]by liquid-phase epitaxy (LPE). This is followed by forming a layer of Zn-doped Al.sub.0.35 Ga.sub.0.65 As (p-type) as a p-type active layer to a thickness of 2-3 microns, and then a layer of Te-doped Al.sub.0.75 Ga0.25As (n-type) as an n-type cladding layer to a thickness of 50 microns. Next, a GaAs substrate-selective etchant (e.g., NH.sub.4 OH:H.sub.2 O.sub.2 =1.7) is used to remove the light-absorptive GaAs substrate, thereby providing a high-intensity LED chip.
In a case where an AuZn electrode is formed on the layer of Zn-doped Al.sub.0.75 Ga.sub.0.25 As in accordance with the above-described prior-art method, an epitaxial layer having a carrier concentration of only 3.times.10.sup.17 cm.sup.-3 is formed stably by liquid-phase epitaxy. Consequently, the contact resistance is high and a variance occurs in the voltage (V.sub.F value) necessary for passing a current of 20 mA in the forward direction of the light-emitting diode (LED). In addition, the lifetime of the light-emitting diode is adversely affected by heat produced when current flows through the contact resistance.
The present invention is intended to solve the foregoing problems and its object is to provide a method of epitaxially growing a substrate for a high-intensity LED in which, with regard to the carrier concentration of the p-type AlGaAs layer that poses problems in terms of forming a stable electrode having little contact resistance and exhibiting ohmic properties, a p-type AlGaAs layer having a carrier concentration of more than 5.times.10.sup.17 cm.sup.-3 is formed in advance by gas-phase epitaxy (MOCVD process, MBE process, etc.), whereby the contact resistance produced between an AuZn electrode and the p-type AlGaAs layer when the electrode is formed can be reduced and variance suppressed.
DISCLOSURE OF THE INVENTION
To this end, a substrate for a high-intensity LED according to the present invention is characterized by comprising a p-type Al.sub.x Ga.sub.1-x As layer (x>0.3) having a carrier concentration of more than 5.times.10.sup.17 cm.sup.-3 and a thickness of 3-7 .mu.m, and an epitaxial layer of a hetero structure formed on the p-type Al.sub.x Ga.sub.1-x As layer, and a method of epitaxially growing the substrate is characterized by comprising a first step of forming a p-type Al.sub.x Ga.sub.1-x As layer (x>0.3) having a carrier concentration of more than 5.times.10.sup.17 cm.sup.-3 on a GaAs substrate to a thickness of 3-7 .mu.m by gas-phase epitaxy, a second step of forming an epitaxial layer of a hetero structure by liquid-phase epitaxy, and a third step of removing the GaAs substrate.
The substrate for a high-intensity LED and the method of epitaxially growing the substrate according to the present invention are based on the fact that, in using an AuZn alloy or the like as the ohmic electrode of the p-type Al.sub.x Ga.sub.1-x As layer, the higher the carrier concentration of this layer, the smaller the contact resistance and the lower the applied voltage (V.sub.F) necessary for passing a forward current of 10 mA. Joint use is made of gas-phase epitaxy and liquid-phase epitaxy. A layer having a carrier concentration three to five times that of an epitaxial layer formed by liquid-phase epitaxy (LPE) can be realized with excellent reproducibility by gas-phase epitaxy (MOCVD process, MBE process, etc.). By utilizing this p-type Al.sub.x Ga.sub.1-x As layer as an e
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Hearn Brian E.
Mitsubishi Kasei Corp.
Mitsubishi Monsanto Chemical Co.
Wilczewski M.
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