Single-crystal – oriented-crystal – and epitaxy growth processes; – Forming from vapor or gaseous state – With decomposition of a precursor
Reexamination Certificate
2000-02-08
2004-02-24
Kunemund, Robert (Department: 1765)
Single-crystal, oriented-crystal, and epitaxy growth processes;
Forming from vapor or gaseous state
With decomposition of a precursor
C117S090000, C117S104000, C117S952000
Reexamination Certificate
active
06695913
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to III-Nitride optoelectronic semiconductor devices, such as light-emitting diodes and laser diodes, and methods of making such devices. It will be well understood by those skilled in the art that a III-Nitride optoelectronic semiconductor device comprises a Group III-V semiconductor compound in which the Group V element is Nitrogen or Nitride containing.
BACKGROUND OF THE INVENTION
Optical data storage technology is capable of storing data, such as audio or video information, at very high densities, and has many applications in both consumer and professional fields. As is well known, such optical data storage technology is used in the reading and writing of compact disks (CD), as well as in the reading and writing of the more recently developed digital video disks (DVD). The introduction of the DVD has resulted in an increase in data storage capacity of more than ten times as compared with the CD, this increase having been brought about by a combination of tighter system tolerances and a decrease in the laser wavelength used to read or write information on the disk, for example from 780 nm to about 650 nm. Further increases in data storage capacity are realisable if the laser wavelength is further reduced to the blue and ultraviolet (UV) parts of the spectrum.
There are two groups of semiconductor compounds and alloys which are capable of emitting light in the blue and UV parts of the spectrum. These are the Group II-VI semiconductor materials denoted generally as (Zn, Mg) (S, Se), where such notation indicates the different compounds formed by combining either Zinc (Zn) or Magnesium (Mg) with Sulphur (S) or Selenium (Se), and Group III-V semiconductor materials from the alloy system denoted by (Al, Ga, In)N, where such notation indicates the alloys formed by combining Aluminium (Al), Gallium (Ga) or Indium (In) with Nitrogen (N)). The former group is most suited to emission in the blue-green part of the spectrum, whilst alloys and compounds of the latter group are particularly suited to emission in a wavelength range spanning orange, through blue to UV.
Progress in the development of Group II-VI semiconductor materials for use in light-emitting devices has resulted in the announcement of 100 hours cw operation of a blue-green laser diode (LD) by S. Taniguchi et al, Electron. Letters, 32, 552 (1996). Whilst this is an impressive achievement, progress in the development of Group III-V semiconductor materials has been even more significant over the last few years. In 1994, the successful realisation of a (InGa)N/(AlGa)N double heterostructure, high brightness blue light-emitting diode was reported by S. Nakamura et al, Appl. Phys. Lett., 64, 1687 (1994). This was followed in 1995 by an announcement of the successful realisation of high brightness blue and violet light-emitting diodes by S. Nakamura et al, Appl. Phys. Lett., 67, 1868 (1995), based on the use of (InGa)N quantum wells (QW) in the active region of the diode. In 1996, pulsed operation at room temperature of an (InGa)N QW laser diode was reported by S. Nakamura et al, Jpn. J. Appl. Phys., 35, L74 (1996). Recently the pulsed operation of an (InGa)N QW laser diode has been announced in Toshiba Corporation, Press Release, Sep. 11, 1996, and the cw operation at room temperature of a 412 nm (InGa)N MQW laser diode has been announced by S. Nakamura et al, late news paper at the IEEE-LEOS Annual Meeting, Boston, November 1996.
These reported results have led to considerable interest being shown in the growth of III-Nitride semiconductor materials and the fabrication of light-emitting diodes and laser diodes based on such materials. Such materials have mainly been produced by the method of epitaxial growth known as Metal Organic Chemical Vapour Deposition (MOCVD) which is also known as Metal Organic Vapour Phase Epitaxy (MOVPE). However it should be noted that such materials can also be produced by the epitaxial growth method known as Molecular Beam Epitaxy (MBE) as reported by, for example, R. J. Molnar et al, Appl. Phys. Lett., 66, 268 (1995). This approach has resulted in the achievement of p-type doping and weak electroluminescence (EL) at room temperature from both GaN homojunction light-emitting diodes and (InGa)N/GaN heterojunction light-emitting diodes. Whilst the results obtained from the semiconductor materials produced by the MBE growth method are currently inferior to the results obtained from semiconductor materials produced by the MOCVD growth method, there are potential advantages in producing such semiconductor materials using the MBE growth method due to the fact that the temperature difference between the growth temperatures of (InGa)N and GaN (or (AlGa)N) is smaller when the MBE growth method is used than when the MOCVD growth method is used, as will be described in more detail below.
A significant problem in the epitaxial growth of III-Nitride semiconductor materials is the hetero-epitaxial nature of the growth process. GaN semiconductor material is only available in non-commercially viable pieces of a few millimeters in dimension so that most growth of GaN is carried out on a Sapphire substrate. Alternative substrate materials have been tried, such as Silicon Carbide (SiC), various oxides such as Lithium Gallate, and Spinel. Without exception, GaN is lattice mismatched from these substrates. For example, the lattice constant of Sapphire is approximately 12.5% larger than that of GaN, and this leads to the generation of many defects at the interface between the GaN and Sapphire. However it appears that GaN is much more fault tolerant than other Group III-V semiconductor materials, and GaN-based light-emitting diodes can operate successfully for extended periods even where there are approximately 10
10
cm
−2
defects in the material. Additionally the differential thermal expansion between the epilayer and the substrate can lead to the generation of dislocations in the layers of the device if the strain energy is not accommodated elastically.
Until commercially viable GaN substrates become available, such problems of hetero-epitaxy and the resulting dislocations that it introduces seem unavoidable. Meanwhile one empirical solution is to grow a sufficiently thick layer of GaN (on a suitable buffer layer) until the layer becomes fully relaxed. Further layers can then be deposited epitaxially onto the layer with the GaN lattice constant. It is also likely that many of the dislocations that are introduced at the substrate-buffer interface will have turned over, and will not therefore penetrate through the whole of the GaN layer if it is sufficiently thick.
A further problem in the growth of III-Nitride semiconductor materials is a function of the design of the light-emitting diode structure used.
FIG. 1
diagrammatically illustrates the light-emitting diode structure used by S. Nakamura et al, Appl. Phys. Lett., 64, 1687 (1994) as reported above. This structure was produced using a MOCVD growth method. A GaN buffer layer
2
of a thickness of about 300 Å was grown on a Sapphire substrate
1
at about 510° C., followed by a n-doped GaN contact layer
3
of a thickness of about 4 &mgr;m, a n-doped (AlGa)N cladding layer
4
of a thickness of about 1.5 &mgr;m, and a Zn-doped (InGa)N active layer
5
of a thickness of about 500 Å. After growth of the active layer
5
, p-doped cladding and contact layers
6
and
7
of (AlGa)N and GaN were grown to thicknesses of about 0.15 &mgr;m and 0.5 &mgr;m respectively, and finally a n-type electrode
8
and p-type electrode
9
were evaporated onto the n-doped contact layer
3
and the p-doped contact layer
7
.
Furthermore
FIG. 2
shows a graph of the variation of the lattice constant a against the band gap energy for the quaternary system (Al, Ga, In) N. In the light-emitting diode structure of
FIG. 1
, the In mole fraction in the active layer
5
of the device is approximately 0.06 whilst the Al mole fraction in the surrounding cladding layers
4
and
6
is approximately 0.15. It will be appreciated from
Kunemund Robert
Sharp Kabushiki Kaisha
LandOfFree
III-Nitride optoelectronic semiconductor device containing... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with III-Nitride optoelectronic semiconductor device containing..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and III-Nitride optoelectronic semiconductor device containing... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3285856