United States Patent [t9J
`Stevenson et al.
`
`[76]
`
`[54] GALLIUM NITRIDE
`MET AL-SEMICONDUCTOR JUNCTION
`LIGHT EMITTING DIODE
`Inventors: David A. Stevenson, 331 Lincoln
`Ave., Palo Alto, Calif. 94301;
`Walden C. Rhines, 9321 Forest Ln.,
`Apt. I 096, Dallas, Tex. 85231;
`Herbert P. Maruska, 2326
`California St., No. 39, Mountain
`View, Calif. 94040
`Mar. 12, 1973
`(22] Filed:
`[21 J Appl. No.: 340,539
`
`(52] U.S. Ct .. .. 313/499, 317/235 UA, 317/235 AD
`lnt.·cr ........................................ ~ .. H05b33/14
`[51)
`[58) Field of Search ....... ... 313/108 D; 317/235 UA,
`317/235 AD; 331/94.5 H
`
`[ 56 I
`
`3,404,305
`
`References Cited
`UNITED STATES PATENTS
`10/1968 Wright. ........................... 313/108 D
`
`3,819,974
`[II]
`[451 June 25, 1974
`
`3,462,630
`
`8/1969 Cuthbert et al. ................ 313/108 D
`
`Primary Examiner-Herman Karl Saalbach
`Assistant Examiner- Siegfried H. Grimm
`Attorney, Agent, or Firm-Flehr, Hohbach, Test, Al(cid:173)
`britton & Herbert
`
`(57]
`
`ABSTRACT
`
`A light emitting diode comprising a first layer of gal(cid:173)
`lium nitride, a second, substantially intrinsic layer of
`magnesium doped gallium nitride forming a junction
`therewith, a metallic rectifying contact to the second
`layer, an ohmic contact to the first layer, and means
`for applying a voltage across said contacts and said
`junctions whereby to bias the devic,e and generate
`light.
`
`4 Claims, 7 Drawing Figures
`
`18
`
`INDIUM
`CONTACT -..1,L--,4----1-"'"'~~~~~ ..... ---
`
`SAPPHIRE
`SUBSTRATE
`
`n-GaN
`
`i-Ga N: Mq
`
`INDIUM
`CONTACT
`
`(cid:47)(cid:50)(cid:58)(cid:40)(cid:54) 1032, Page 1
`VIZIO Ex. 1032 Page 0001
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`

`PATENTEDJUM25 l974
`
`3~"8 19~97 4
`
`SH(El 1 Of 2
`
`A tt------_------it"
`B t~-~t:~
`
`(14
`J
`
`..___ ____ FIG.
`15
`
`I
`
`16
`
`-'----12
`r-r--.-~---------t
`
`II
`
`13
`
`FIG. 2
`
`·
`
`18
`
`INDIUM
`CONTACT--i.~----..r~..........-..........-..........-~
`
`SAPPHIRE
`SUBSTRATE
`
`n-GaN
`
`i-Ga N: Mg
`
`INDIUM
`CONTACT
`
`FIG. 3
`
`(cid:47)(cid:50)(cid:58)(cid:40)(cid:54) 1032, Page 2
`VIZIO Ex. 1032 Page 0002
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`

`

`PATENTEfJJUN25 ~74
`
`SHEET 2 OF 2
`
`.
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`3,819,974
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`2.0
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`3.0
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`h-v (eV)
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`2. 8 8~-r---.-----,.--....----.-----,,......,.
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`0
`4
`.8
`1.2 1.6 2.0 2.4
`INPUT CURRENT (mA)
`
`FIG. 4
`
`F IG. 5
`
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`1-
`(/) ~z
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`:::, -
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`0.4
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`
`-8.0
`
`0
`VOLTS
`
`+8.0
`
`FIG. 6
`
`FIG. 7
`
`(cid:47)(cid:50)(cid:58)(cid:40)(cid:54) 1032, Page 3
`VIZIO Ex. 1032 Page 0003
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`

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`3,819,974
`
`2
`the n-type layer is typically I 00 microns with an ap(cid:173)
`proximate range of thickness between 50 and 200 mi(cid:173)
`crons(µ.). The gallium nitride is formed by the reaction
`
`1
`GALLIUM NITRIDE METAL-SEMICONDUCTOR
`JUNCTION LIGHT EMITrlNG DIODE
`GOVERNMENTCOITTRACT
`The invention described herein was made in the per- 5
`GaCl + NH3 = GaN + HCl + H2
`formance of work under a research grant from the Ad(cid:173)
`After growth of the region 12, the atmosphere is doped
`vanced Research Projects Agency.
`by introducing metallic magnesium while the layer is
`BACKGROUND OF THE INVENTION
`being grown to form a magnesium doped gallium ni-
`This invention relates generally to light emitting di- JO tride layer 13. The dopant atoms compensate the nor-
`mally n-type growth to form a substantially intrinsic
`odes and more particularly to a violet light emitting di-
`GaN:Mg layer 13. The layer 13 forms an i-n junction
`ode.
`14 with the layer 12. The magnesium is added by plac-
`Undoped gallium nitride always occurs highly n-type
`ing magnesium in a graphite crucible and maintaining
`(n > 1018 cm-3 ) and thus far has not been made con-
`ducting p-type. However, a deep acceptor such as zinc 15 it at approximately 710°C while passing thereover ni-
`trogen gas. This transports the elemental magnesium
`has been utilized to compensate the donors and pro-
`atoms into the growth zone where they deposit as an
`duce insulating gallium nitride crystals. This dopant
`impurity or dopant with the gallium nitride to form the
`can be introduced during the growth of the gallium ni-
`intrinsic GaN:Mg region 13. The introduction of Mg
`tride crystal. When the dopant is introduced after ini-
`tial deposition of undoped material, an i-n junction is 20 produces an energetically deep (many kT above the va-
`Jenee band) acceptor level which compensates the na-
`fonned. In the prior art, red, yellow, green and blue
`tive donors in GaN, thus making it intrinsic. The thick-
`light emitting diodes have been obtained with zinc
`ness of this intrinsic, i, layer 13 is typically I 0µ, with a
`doped insulating regions forming i-n junctions.
`possible range of 5-20µ. and the magnesium concentra(cid:173)
`OBJECTS AND SUMMARY OF THE INVENTION 25 tion in the layer is typically 0. 15 weight percent ( I 020
`) as determined by electron microprobe
`atoms cm-3
`It is a general object of the present invention to pro-
`analysis, with a possible range of 5 x 10 19 to 1021 atoms
`vide a violet light emitting diode.
`cm- 3•
`It is another object of the present invention to pro-
`After the formation of the slice shown in FIG. IC, the
`vide a violet light emitting diode formed by a rectifying
`metal contact to an intrinsic magnesium doped layer of 30 slice is cut up or diced to form devices of predeter-
`mined siz.e. A metal layer 17, 100µ. thickness or larger,
`gallium nitride forming a junction with a gallium nitride
`is deposited onto the surface of the intrinsic layer to
`layer.
`form a second m-i rectifying junction 15 with the intrin-
`The foregoing and other objects of the invention are
`sic layer. Various metals and deposition techniques
`achieved by a light emitting diode comprising a first
`layer of gallium nitride, a second layer of magnesium 35 may be utilized. For example, an indium-mercury amal-
`garn may be painted on the surface of the magnesium-
`doped gallium nitride forming a junction therwith, a
`doped gallium nitride region 13. The chip is then
`metal layer forming a rectifying junction with the sec-
`heated for about a minute at 400°C to drive off the
`ond layer, and means for applying a voltage across said
`mercury. This leaves a solid indium layer. Other metals,
`junctions to generate and emit light.
`40 such as Al, Au, Pt and Ag, may be deposited as a layer
`BRIEF DESCRIPTION OF THE DRAWING
`17 by vacuum evaporation, chemical vapor deposition
`or by sputtering. Similar techniques are used to pro-
`FIG. I shows the steps in' the growing of a layered de-
`duce a metal ohmic contact 16 on the edge of the n
`vice in accordance with the invention.
`layer 12. A variant in this structure consists of the re-
`FIG. 2 shows the step of forming ohmic contacts with
`45 movaJ of a portion of the sapphire substrate or the in-
`the device regions.
`trinsic layer whereby contact may be made to a portion
`FIG. 3 shows a device in accordance with the inven-
`of the surface of the n-type layer 16.
`tion mounted in a metallic support.
`cThe device may be placed in a holder 18 such as
`FIG. 4 shows the electroluminescence spectrum with
`shown in FIG. 3 comprising a cup-shaped metal holder.
`forward bias.
`FIG. S shows the shift of forward bias electrolumi- 50 One surface of the indium contact 17 forms ohmic con-
`nection with the holder. Leads 19 and 21 provide elec-
`nescent peak with input current.
`trical connection to the indium contact 16 and holder
`FIG. 6 shows the electroluminescence spectrum with
`18 for application of voltage across the region 13 and
`reverse bias.
`junctions 14 and IS.
`FIG. 7 shows typical current voltage characteristics
`In a device constructed in accordance with the fore-
`for the device.
`going, electroluminescence or light generation is ob(cid:173)
`DESCRIPTION OF PREFERRED EMBODIMENT
`tained both with forward and reverse bias, that is, with
`the i-layer bias either positive or negative. The forward
`Referring to FIG. 1, the steps of forming a junction
`gallium nitride light emitting diode are illustrated. A 60 bias voltage is more efficient. In the forward direction,
`substantial conduction begins at IO volts and the violet
`wafer or slice of single crystal flame-fusion-grown sap-
`light is readily seen in a well lit room at 20 volts. Under
`phire may be used as the substrate 11. A layer of highly
`reverse bias, conduction occurs in 40 - 60 volt range
`n-type gallium nitride 12 is formed on one surface of
`and produces a greenish light. Emission under forward
`the wafer 11 by transporting gallium as its gaseous
`monochloride and introducing nitrogen into the growth 65 bias electroluminescence peaked in the region of 2.86
`- 2.98 electron volts in various samples. The spectral
`zone in the form of ammonia, both at an elevated tern-
`width of half maximum is about 400 meV ~ A typical
`perature (approximately 900°-950°C.) whereby .there
`spectrum is shown in FIG. 4, It is seen that the peak
`is epitaxially grown the GaN layer 12. The thickness of
`
`55
`
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`3,819,974
`
`4
`to develop different colors for a~thetic purposes, but
`also to produce light in a spectral !'allge of greater sen(cid:173)
`sitivity for the human eye. By use of different phos(cid:173)
`phors, all the primary colors may be developed from
`s this same basic device. An array of such devices may
`be used for color display systems; for example, a solid
`state TV screen.
`We claim:
`l. A light emitting diode comprising a first region of
`Jo gallium nitride, a second region of magnesium doped
`gallium nitride on one surface thereof forming a recti(cid:173)
`fying junction therewith, a metal forming a rectifying
`j unction with the second region; !IJld means forming
`ohmic contact to said first regiorr whereby a voltage
`1 s can be applied to said metal and said means forming
`· ohmic contact to apply a voltage across said junctions:
`
`3
`shifts to shorter wavelength with increasing current
`until a saturation value is reached; an example of the
`saturation is shown in FIG. 5 wherein emission peak
`versus input current is shown. The voltage current
`characteristics of a device constructed in accordance
`with the foregoing is shown in FIG. 7. The reverse bias
`light emission is shown in FIG. 6. Although the emitted
`light appears uniform to the unaided eye, it actually
`consists of an array of spots in the size range of 5 - 25 µ.
`with an inter-spot distance of I 00 - 200µ., as deter(cid:173)
`mined by high resolution optical microscopy. The lumi(cid:173)
`nescence is believed to be the result of field-emission
`of electrons trapped by the Mg acceptor levels, with
`subsequent recombination of electrons to the then
`empty levels left by the field-emission. This process oc(cid:173)
`curs in regions of high electric field. It has been deter(cid:173)
`mined by scanning electron microscopy that a high
`2. A light emitting diode as in claim l wherein said
`electric field occurs at the i-n junction with forward
`magnesium has a concentration in the range of 5 x I 0 19
`bias, and at the m-i junction with reverse bias. The fact
`that these two junctions are expected to have different 20 to I 0 21 atoms/cm3•
`3. A light emitting diode as in claim 2 wherein said
`characteristics is responsible for the shift in the peak of
`second layer has a thickness in the range of 5 to 20 mi(cid:173)
`the luminescence in going from forward to reverse bias.
`c rons.
`4. The method of generating violet light which com-
`Thus, it is seen that there has been provided an im-
`proved light emitting diode capable of emitting light in 25 prises the steps of trapping electrons in magnesium ac-
`ceptors in an intrinsic gallium nitride layer, causing re-
`the violet region of the spectrum. This device may be
`moval of said e lectrons from said acceptors by applying
`used as a source of violet light for applications where
`.an electric field of sufficient magnitude to remove the
`this spectral range is appropriate. This light may be
`electrons, and causing electrons to recombine with said
`converted to lower frequencies (lower energy) with
`good conversion efficiency using organic and inorganic 30 magnesium acceptors whereby to generate violet light.
`* * * * *
`phosphors. Such a conversion is appropriate not only
`
`35
`
`40
`
`45
`
`so
`
`55
`
`60
`
`65
`
`r·
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