GB2343294A - Lattice-matched semiconductor devices - Google Patents

Lattice-matched semiconductor devices Download PDF

Info

Publication number
GB2343294A
GB2343294A GB9823778A GB9823778A GB2343294A GB 2343294 A GB2343294 A GB 2343294A GB 9823778 A GB9823778 A GB 9823778A GB 9823778 A GB9823778 A GB 9823778A GB 2343294 A GB2343294 A GB 2343294A
Authority
GB
United Kingdom
Prior art keywords
semiconductor device
gabn
sic
layer
gan
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB9823778A
Other versions
GB9823778D0 (en
Inventor
Wyn Meredith
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Sharp Corp
Original Assignee
Sharp Corp
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Sharp Corp filed Critical Sharp Corp
Priority to GB9823778A priority Critical patent/GB2343294A/en
Publication of GB9823778D0 publication Critical patent/GB9823778D0/en
Publication of GB2343294A publication Critical patent/GB2343294A/en
Withdrawn legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/26—Materials of the light emitting region
    • H01L33/30—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table
    • H01L33/32—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table containing nitrogen
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02367—Substrates
    • H01L21/0237—Materials
    • H01L21/02373—Group 14 semiconducting materials
    • H01L21/02378—Silicon carbide
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
    • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
    • H01L21/02104—Forming layers
    • H01L21/02365—Forming inorganic semiconducting materials on a substrate
    • H01L21/02518—Deposited layers
    • H01L21/02521—Materials
    • H01L21/02538—Group 13/15 materials
    • H01L21/0254—Nitrides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/005—Processes
    • H01L33/0062—Processes for devices with an active region comprising only III-V compounds
    • H01L33/0066—Processes for devices with an active region comprising only III-V compounds with a substrate not being a III-V compound
    • H01L33/007—Processes for devices with an active region comprising only III-V compounds with a substrate not being a III-V compound comprising nitride compounds
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/10—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a light reflecting structure, e.g. semiconductor Bragg reflector
    • H01L33/105—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a light reflecting structure, e.g. semiconductor Bragg reflector with a resonant cavity structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S5/00—Semiconductor lasers
    • H01S5/30—Structure or shape of the active region; Materials used for the active region
    • H01S5/32—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures
    • H01S5/323—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser
    • H01S5/32308—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser emitting light at a wavelength less than 900 nm
    • H01S5/32341—Structure or shape of the active region; Materials used for the active region comprising PN junctions, e.g. hetero- or double- heterostructures in AIIIBV compounds, e.g. AlGaAs-laser, InP-based laser emitting light at a wavelength less than 900 nm blue laser based on GaN or GaP

Landscapes

  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Computer Hardware Design (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Chemical & Material Sciences (AREA)
  • Materials Engineering (AREA)
  • Semiconductor Lasers (AREA)
  • Led Devices (AREA)

Abstract

A semiconductor device 40 comprises a SiC layer 42 and at least one further layer 46, 48, 50 grown, directly or indirectly on the SiC layer, wherein said further layer is a ternary or quaternary composition of the (GaInAlB)N system, comprises boron, and is substantially lattice matched to the SiC layer 42. The device may be a light emitting device such as a laser diode, an electronic device such as a laser diode, or a high reflectance mirror structure. The use of alternatives for the SiC substrate layer is also disclosed.

Description

Semiconductor Devices The invention relates to semiconductor devices, and particularly to light emitting devices which operate in the blue-LTV range. The devices described have applications in various fields, including optical storage media (such as compact discs), optical telecommunications and datacoms, visible display systems and fluorescence lighting.
Blue laser diodes based on the nitride materials system will first be discussed.
The III-V nitride system (Ga, Al, ln) N is now established in the blue/violet LED market and is the most likely candidate for the first mass produced blue laser diodes (LDs), with commercialisation likely by the end of 1998 (see for example S. Nakamura, M.
Senoh, S. Nagahama, N. Iwasa, T. Yamada, T. Matsushita, H. Kityoku, Y. Sugimoto, T.
Kozaki, H. Umemoto, M. Sano, K. Chocho, Appl. Phys. Lett. 72 (2) (1998) 211).
Although the characteristics of the nitride LDs have improved remarkably in the two years since lasing was first observed in 1996, state of the art devices are still grown on mismatched substrates such as (0001) sapphire (mismatch=16.1%) and (0001) 6H-SiC (mismatch = 3.5%). By way of explanation, such mismatching occurs when the interatom spacing in the lattice of the host substrate differs from that of the layers grown on the substrate. The term"growing"refers to the careful laying down of layers of atoms.
With such large substrate mismatches the nitride material quality is poor in comparison with devices in established materials systems such as GaAs/AlGaAs. The most recent technological advances have enabled the extension of continuous wave (cw) lifetimes of GaN LDs to 10,000 hrs and are the results of attempts to decrease the mismatch dislocation density in the device. Mismatching of substrates tends to produce imperfections/dislocations in the layers above the substrate, as a mechanism of strain relief in the layers.
In the latest LDs from Nichia, AlN/GaN strained layer superlattices replaced mismatched AIGaN cladding layers in the structure. Previously these cladding layers introduced cracks and misfit dislocations into the structure when the AIGaN layer was grown thicker than its critical thickness on GaN. See K. Ito, K. Hiramatsu, H. Amano, I. Akasaki, J. Cryst. Growth 104 (1990) 533.
The devices are now grown on patterned sapphire substrates. The so called Epitaxially Laterally Overgrown GaN (ELOG) (See A. Usui, H. Sunakawa, A. Sakai, A. A.
Yamaguchi, Jpn. J. Appl. Phys. Part 2 Vol. 36 (1997) L899.) substrate is a (0001) c-face sapphire substrate with a jim thick layer of GaN, then a 0.111m thick Si02 striped mask and finally 10pm thick GaN layer grown on top. In the region above the Si02 stripes the defect density in the thick GaN is almost zero, and in the region between the stripes the defect density is 108 cni 2, typical of GaN grown directly on sapphire. The laser cavity is then defined in the region of zero defects.
The reduction of defects in the cavity area is the largest contributory factor in the extension of the lifetime from 30hrs to-10, 000hrs. Defects tend to increase the operating and threshold current of a device, and so if the device has a fixed resistance R, then increasing the operating current increases the power dissipation in the device. So indirectly, a high defect density generates more heat in the device.
Defects tend to propagate throughout the device under extreme temperature conditions.
If defects propagate into the active region, this results in a larger operating current and maybe voltage. This leads to increased power dissipation in the device, which leads to an increased propagation of more defects. This effect is called"thermal runaway"It can result in such a large number of defects in the active region that lasing action is quenched, and the device can"die"catastrophically.
It would therefore be desirable to reduce defects without the complications in the growth procedure and the extra processing steps described above. The most obvious way to do this is to revert to the conventional method of realising defect free material by growing epitaxial layers lattice matched to a suitable substrate. The invention provides the addition of boron to the (GaAl) N system, which allows a range of materials and devices that are lattice matched to 6H-SiC substrates, while also extending the practical operating wavelength into the UV range (fig. 1).
The properties of Boron Nitride will be discussed briefly.
Boron nitride can exist in numerous forms, ranging from diamond-like cubic and wurtzite to graphite-like hexagonal and rhombohedral structures. The most commonly occurring structure is hexagonal (h-BN), referred to as pyrolytic BN when formed by chemical vapour deposition (CVD). The wurtzite form of BN (w-or y-BN), is a high pressure, relatively rare form, metastable at room temperature and pressure. See W. R.
L. Lambrecht, B. Segall,'Properties of Group III Nitrides'J. H. Edgar, INSPEC publications (1994) 133. Since the (GaAlIn) N system is wurtzite when grown on sapphire and 6H-SiC, it is necessary to consider the properties of w-BN when predicting (GaAIB) N alloy properties, outlined in table 2.1. These results are provided in the INSPEC reference given above, and also in A. V. Kurdyumov, V. L. Solozhenko, W. B.
Zelyavsky I. A. Petrusha, J. Phys. Chem. Solids 54 (1993) 1051.
Indirect bandgap s. av Direct bandgap-8. 5eV* r a axis lattice constant 2.55A Thermal expansion 2x10 coefficient at 300K I I Table 2.1 properties of w-BN The values marked"*"are undetermined experimentally. The values given are averages of several theoretical predictions summarised by Lambrecht (see INSPEC reference mentioned above).
The Epitaxial growth of (GaAIB) Nitride alloys is now discussed.
Interest in the (GaAIB) N system has emerged only very recently as a result of the realisation of practical GaN based blue emitters. The first suggestion of the use of small amounts of boron in GaAlN to lattice match to SiC was by Sakai in 1993 (See S. Sakai, Y. Ueta, Y. Terauchi, Jpn. J. Phys. 32 (1993) 4413, but the first epitaxial growth of a mixed alloy was not reported until 1996. See M. Haruyama, T. Shirai, H. Kawanishi, Y. Suematsu, Proc. of the International Symposium on Blue Lasers and LEDs, Chiba, Japan, (1996) 106. Since then there have been several studies to investigate the solubility of boron in GaN and A1N and the resulting crystal structure, but generally attempts to incorporate significant amounts of boron ( > 15%) have failed.
Polyakov grew GaBN (See A. Y. Polyakov, M. Shin, M. Skowronski, D. W. Greve, R.
G. Wilson, A. V. Govorkov, R. M. Desrosiers, J. Electronic Materials 26 3 (1997) 237.) and AIBN (see A. Y. Polyakov, M. Shin, W. Qian, M. Skowronski, J. Appl, Phys. 81 4 (1997) 1715.) ternaries (ie. compound semiconductors formed from three elements) by Organo-Metallic Vapour Phase Epitaxy (OMVPE) on A1N buffer layers grown on sapphire substrates. The maximum incorporation of B in GaN was 7% as measured by X-ray diffraction (XRD) (see Figure 2). The data points extend only to 0.07 on the lower line), but attempts to incorporate B in A1N were less successful; only 1% incorporation was achieved before phase separation into w-Alo. 99Bo. olN and w-BN (see Figure 2, top line). Haruyama achieved a 5% incorporation of B in A1N grown by OMVPE on 6H-SiC, but it is unclear whether the structure was zincblende or wurtzite, and little information is given regarding the crystalline quality of the material (see Haruyama reference given above). Shibata grew GaN/AlBN heterostructures by OMVPE and detected single crystal Ga0 87Bo 13N using XRD and PL measurements (see M. Shibata, M. Kurimoto, J. Yamamoto, T. Honda, H. Kawanishi, Proceedings of ICNS 97, Tokushima, Japan). Vezin et al reported on the first attempts to grow Gal-xBxN by MBE using an elemental boron source (see V. Vezin, S. Yatagai, H. Shiraki, S. Uda, Jpn. J. Appl. Phys. Part 2 Vol. 36 (1997) L1483). Single crystal wurtzite material was grown successfully up to a boron mole fraction of 0.0456, as measured by XRD (See Figure 3). The structure of the alloy was found to be very sensitive to the growth parameters. Mixed zincblende and wurtzite material was observed under Ga rich conditions, or at substrate temperatures below 790 C. The crystalline quality of the layers degraded as the boron content increased, as illustrated by the increase of the XRD FWHMs (Full Width at Half Maximum) from 4 min for GaN to 43 min for Gao. 95sBo. o45N.
Paisley obtained similar results when a granded GaBN epilayer was grown on a SiC substrate by Molecular Beam Epitaxy (MBE) (see M. J. Paisley, Z. Sitar, Benda Yang, R. F. Davis, J. Vac. Sci. Technol. B8 2 (1990) 323). The layer was found to be a mixture of cubic wurtzitic phases with a high dislocation density as a result of an estimated 19.8% mismatch with the substrate. However, the purpose of the layer was as a graded buffer layer for the growth of crystalline BN, and so the growth parameters were not optimised for the ternary alloy.
The above references illustrate initial attempts to grow boron containing nitride alloys, and show that it is possible to overcome the problem of phase stability of the wurtzitic form by careful attention to the optimisation of growth conditions. Improvements in the alloy quality and extension of the range of possible composition can be expected with further investigation of the MBE and OMVPE growth parameters.
According to the invention there is provided a semiconductor device, such as a laser diode, comprising a SiC layer and at least one further layer grown, directly or indirectly on the SiC layer, wherein said further layer is a ternary or quaternary composition of the (GaInAIB) N system, comprises boron, and is substantially lattice matched to the SiC layer.
The use of nitride ternaries containing boron in the structure results in a device with a low misfit defect density similar to current 10,000 hr lifetime nitride devices. However, the use of patterned substrates and thick buffer layers is avoided, thus reducing the number of processing steps and the cost of production, for example of nitride LDs.
The semiconductor device may be a separate confinement heterostructure (SCH) laser diode.
The laser diode may comprise an active layer formed from alternating layers of GaN and GaBN.
The laser diode may comprise an active layer formed from alternating layers of GaBN and GaInN.
The laser diode may comprise a waveguide layer formed from GaBN.
The laser diode may comprise a cladding layer formed from A1BN.
The SiC layer may form the substrate of the laser diode.
The semiconductor device may be a surface emitting laser.
The surface emitting laser may comprise a first reflector formed from alternating layers of GaBN and A1BN.
The surface emitting laser may comprise a second reflector formed from alternating layers of GaBN and A1BN.
Said first reflector may contain more alternating layers of GaBN and A1BN than said second reflector.
The surface emitting laser may further comprise an active layer formed from alternating layers of GaInN and GaBN.
Said active layer may be sandwiched between two spacer layers formed from GaBN.
The SiC layer may form the substrate of the surface emitting laser.
The semiconductor device may be a light emitting diode.
The semiconductor device may be an electronic device, such as a transistor.
The transistor may be, for example: a Heterobipolar Transistor (HBT), a Heterojunction Field Effect Transistor (HFET), a Metal-Semiconductor Field Effect Transistor (MESFET), a Metal-Insulator-Semiconductor Field Effect Transistor (MISFET), or a Modulation Doped Field Effect Transistor (MODFET) For efficient room temperature (RT) operation a SCH laser diode structure must provide enough quantum well confinement to prevent carrier leakage at the desired operating temperature. An embodiment of the invention described below gives approximately 0.9eV confinement between the QW and barrier and 2.9eV confinement between the QW and the cladding region. Even assuming an error of 20% in these values to allow for uncertainty in the bandgap of w-BN, deviation of the band offsets from the 60: 40 rule and the error in using the unstrained value of the bandgap of the GaN QW, the structure still has greater confinement than current nitride laser diodes by a factor of 4.
Boron containing devices should therefore be able to operate at higher temperatures compared to (AIGaIn) N devices.
The invention will now be more particularly described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a graph of lattice constant versus bandgap for the (GaAlBIn) Nitride material system, highlighting ternary compounds lattice matched to 6H-SiC ; Figure 2 is a graph of bandgap versus composition for GaBN and A1BN ; Figure 3 is a (prior art) graph of boron cell temperature versus composition for GaBN grown by MBE; Figure 4 is a schematic representation of a prior art (InGaAI) N separate confinement heterostructure (SCH) laser diode grown on a mismatched sapphire substrate; Figure 4a is a schematic representation of a (GaAIB) N SCH laser diode according to the invention ; Figure 5 shows estimated valence and conduction band offsets in the (GaAIB) N SCH laser diode structure of Figure 4; Figure 6 shows estimated valence and conduction band offsets in a blue (GaAlB) N SCH laser diode structure according to the invention; Figure 7 shows the refractive indices of GaN, Gao, 83Bo. nN, A1N and Alo. osBo. 95N over the range 350-550nm ; Figure 8 shows theoretical reflectance spectra of Ga0 g3Bo s7N/Alo 9sBo o5Nl6H-SiC B/4 mirror stacks; Figure 9 is a schematic representation of a blue Vertical Cavity Surface Emitting Laser (VCSEL) structure lattice matched to 6H-SiC.
Figure 9a shows the simulated reflectance spectrum for the structure of Figure 9; Figure 10 is a schematic representation of a GaBN/SiC heterobipolar transistor (HBT).
Figure 1 shows how the lattice constant and bandgap vary for different compositions of the lattice in a (GaAlBIn) Nitride system. The four points 2,4,6,8 correspond to InN, A1N, BN and GaN respectively. Boron nitride is labelled w-BN to indicate that its structure is wurtzite. Each of the four metals In, Al, B and Ga lies in Group III of the periodic table, and the non-metal N (nitrogen) lies in group V of the periodic table. At each of the four points 2,4,6 and 8 each metal and N are present in equal quantities.
That is, for each metal atom in the lattice there is a corresponding N atom.
The shaded area 10 which lies between these four points corresponds to different compositions of the lattice, containing two (ternary), three (quaternary) or even four (quintemary) different metals. (The names of these systems include (ie. count) the nonmetal.) However, the metal and non-metal atoms in the lattice are still present in the ratio 50: 50.
In Figure 1 the four lines connecting the four points 2,4,6 and 8 at the perimeter of the shaded area 10 are labelled 12,14,16 and 18, and these correspond to AlInN, BAIN, GaBN and InGaN respectively. For example, as we move along line 12 from point 2 to point 4 we move from InN, through AlInN containing increasing amounts of Al, until we eventually come to AIN at point 4. Halfway along line 12 equal amounts of Al and In are present in the lattice, and this point (labelled 20) therefore corresponds to Al05kosNl the total number of metal atoms being equal to the total number of nonmetal atoms.
Similarly, line 22 corresponds to InBN, and line 24 corresponds to AlGaN.
Point 26 represents silicon carbide, SiC, and the vertical dotted line 28 indicates the lattice constant of SiC. The structure of the SiC is wurtzite, and the stacking order of the Si and C atoms can be described as 6H.
Within the (GaAlBIn) Nitride system of Figure 1 it is possible to form one quintemary system (GaAIInB) N; four quaternary systems; (GaInAI) N, (GaAIB) N, (GaInB) N, and (AlInB) N; six ternary systems (GaIn) N, (GaAI) N, (GaB) N, (InAI) N, (InB) N and (A1B) N; and four binary systems.
The quintemary system is represented by the whole of the shaded area 10 and this overlaps all four quaternary systems. Furthermore, each quaternary system overlaps with two of the other three quaternary systems. For example the quaternary system (Al In B) N corresponds to the area bounded by the (ternary system) lines 14,20 and 22, and this overlaps with both (Ga A1 In) N bounded by lines 12,18 and 24, and (Ga Al B) N bounded by lines 14,16 and 24. For completeness, the quaternary system (Ga In B) N is bounded by lines 16,18 and 22.
Figure 4 is a schematic representation of a prior art (InGaAI) N separate confinement heterostructure (SCH) laser diode 100 grown on a mismatched sapphire substrate 102.
This laser diode is described in, for example, S. Nakamura et al, Applied Physics Letters 69 No. 10 P1477. An active layer 104 is formed from alternating layers of InGaN (which emits in the blue) and GaN (not shown separately) which have different band gaps and hence form a series of quantum wells which allow lasing to take place.
The compositions of the layers forming the active layer 104 are chosen to achieve the appropriate band gaps using information such as that in Figure 1. The active layer 104 is sandwiched between two GaN layers 106 which act as a waveguide to direct light produced in the active layer 104 along the active layer 104 and ultimately out of the device. The waveguide layers 106 are in turn sandwiched between two cladding layers 108 formed from AlGaN.
Ideally the substrate of Figure 4 would be formed of GaN, which would result in the substrate being matched to the layers above (with compositions optimised accordingly).
However, the mismatched sapphire substrate 102 of Figure 4 is used because it is not practical to form the substrate from GaN. At present this is too expensive and the technology is not sufficiently developed.
Figure 4a is a schematic representation of a (GaAB) N SCH laser diode 40 which constitutes a first embodiment of the invention. The laser diode 40 comprises a SiC substrate 42 on which are grown a buffer layer 44 formed from GaBN or A1BN, two cladding layers 46 formed from AIBN, two waveguide layers 48 formed from GaBN, and an active layer 50 formed from a plurality of GaBN barrier layers 52 and GaN quantum well layers 54. Light generated in the active layer 50 is confined to the active layer 50 and the waveguide layers 48. The buffer layer 44 acts to smooth out any roughness of the upper surface of the substrate 50.
It can be seen from Figure 1 that the use of Boron in the layers above the substrate 42, and the choice of SiC as the substrate 42, allow these layers to be lattice matched with the substrate 42. This is advantageous because lattice matching reduces the number of imperfections and dislocations throughout the device, and hence increases the lifetime of the device for the reasons explained above in relation to the reduction of defects in the cavity area.
The ternary compositions for lattice match to 6H-SiC are Gao. s3Bo. l7N and Al095Bo. 05N (+/-0.005). The values used for the a-axis lattice constants of the relevant wurtzite nitride binary compounds are given in table 3.1.
Binary a () w-BN 2. 557 A1N 3. 112 GaN 3. 189 InN 3. 548 6H-SiC 3. 082 Table 3.1 a-axis lattice constants for binary nitride compounds compared to SiC.
The active region of the device is one (or more) GaN quantum well (s) with a barrier of GaBN. The device is lattice matched apart from the quantum well (s), which must be thinner than the critical thickness of GaN on SiC (approximately 30A).
For operation in the blue/violet range of the visible spectrum it is necessary to use a quantum well (QW) material with a smaller bandgap than GaN. This has been achieved by using GaInN as the QW material in all the nitride blue laser diodes demonstrated to date (see S. Nakamura, M. Senoh, S. Nagahama, N. Iwasa, T. Yamada, T. Matsushita, H. Kiyoku, Y. Sugimoto, T. Kozaki, H. Umemoto, M. Sano, K. Chocho, Appl. Phys.
Lett. 72 (2) (1998) 211; P. Kung, A. Saxler, D. Walker, A. Rybaltowski, X. Zhang, J.
Diaz, M. Razeghi, Mrs J. Nitride Semicod. Res. 3 (1998) 1; and G. E. Bulman, K.
Doverspike, S. T. Sheppard, T. W. Weeks, H. S. Kong, H. M. Deringer, J. A. Edward, J. D. Brown, J. T. Swindell, J. F. Schetzina, Elec. Letts. 33 18 (1997) 1556). Long lifetime LDs produced by Nichia use 35A Gao. 85lino. ssN QWs in the active region of the devices, which emit at 396.6nm. An adaptation of the structure in Figure 4 is to replace the GaN QWs with GaInN (which emits in the blue), producing a device that emits at a longer wavelength (around 485nm, which corresponds to"true blue"). The lattice constant of GaInN is larger than that of 6H-SiC (see Figure 1), so to accommodate the extra compressive strain in the QW the lattice constant of the barrier (52) and waveguide (48) layers should be decreased. As an example, for a device that has a 35A Gao. 85lino. 15N QW and a 100A barrier layer, similar to state of the art devices, the composition of the barriers and waveguide layers would be Gao. glBo. i9N for complete strain symmetrisation (see Figure 6).
Figure 5 shows estimated valence and conduction band offsets in the (GaAlB) N laser diode 40 of Figure 4. The cladding layers 46, waveguide layers 48 and active layer 50 are all indicated using the same reference numerals as in Figure 4a. Figure 5 shows the conduction band 60, valence band 62, and the quantum wells formed by the GaBN barrier layers 52 and GaN quantum well layers 54 within the active layer 50. The GaBN barrier layers 52 are referred to as barrier layers because quantum wells are defined between them. The quantum wells are strained because of the different lattice constants of GaN and Gao. g3Bo. nN, as can be seen from Figure 1.
The values shown in Figure 5 are based on an assumption that the bandgap of w-BN is 8.6eV, obtained by extrapolation of GaBN data from Polyakov et al. This is in agreement with the review of theoretical calculations by Lambrecht that predicted the direct bandgap to be between 8 and 8.9eV (see W. R. L. Lambrecht, B. Segall, 'Properties of Group III Nitrides'J. H. Edgar, INSPEC publications (1994) 133). A 60: 40 split of the bandgap difference is assumed to give the conduction and valence band offsets in the schematic, which is a reasonable assumption for III-V materials that form a type I heterostructure. This device is expected to emit in the range 350-360nm, depending on the exact thickness of the GaN QW.
Possible n-type dopants are silicon, zinc or cadmium while possible p-type dopants are magnesium, calcium or carbon.
Figure 6 shows a second embodiment of the invention in which the GaN quantum wells 54 of Figure 5 are replaced by GaInN quantum wells which emit around 3.12eV which corresponds to a blue emission at a wavelength of about 397nm. Complete strain symmetrisation can be achieved by forming the barrier layers 52 and waveguide layers 48 from Gao. 8lBo. i9N.
Shorter wavelength (eg. far UV) devices can be realised with the use of Gal xBxN as the quantum well material with strain balanced Gal yAlyN barriers. For x > 0.17 Gal-XBxN has a smaller lattice constant than 6H-SiC, while Gai. yAlyN has a larger lattice constant than 6H-SiC for all y. A strain balanced active layer with adequate QW confinement can be achieved in a similar manner to the embodiment of Figure 6.
The application of the invention to high reflectance mirrors and VCSEL structures will now be discussed.
High reflectance mirror structures are important for the realisation of nitride devices such as surface emitting lasers (VCSELs) (in which there is no waveguide layer and emission occurs in a direction perpendicular to the active layer), resonant cavity LEDs and Fabry-Perot modulators. Mirrors are grown using alternating layers of high and low refractive index materials which are ? J4n thick, where X is the operating wavelength of the device and n is the refractive index of the layer. Nitride mirror structures have been grown on mismatched substrates using materials such as AlN/GaN on GaAs (see I. J. Fritz, T J Drummond, Elec Letts 31,1, (1995) P68) and Alo4Gao. 6NlAlol2Gaos8N on sapphire (see J. M. Redwing, D. S. Loeber, N. G.
Anderson, M. A. Tischler, J. s. Flynn, Appl. Phys. Lett. 69 1 (1996) 1). The maximum reflectance reported for a nitride mirror stack is R=0.95 (see M. A. Khan, J. N. Kuznia, J. M. Van Hove, D. T. Olson, Appl. Phys. Lett. 59 (1991) 1449), well below that needed for the efficient operation of VCSELs (R > 0.999). Obtaining such a high reflectance mirror using epitaxially grown compounds is difficult since a relatively large refractive index difference between the two materials is required. If the materials are mismatched, then misfit dislocations at mirror interfaces will act as scattering centres, lowering the total reflectance of the structure. Fritz reported that although a 15 period GaN/AIN mirror stack on GaAs had a theoretical peak reflectance value of 0.95, the measured value of such a stack was only 0.90 (see I. J. Fritz, T J Drummond, Elec Letts 31,1, (1995) P68). The difference in reflectance was attributed to variations in the layer thickness throughout the structure and scattering at interface mismatch defects. To obtain a reflectance close to unity, lattice matched materials with the largest difference in refractive index possible are desirable, and these criterion are fulfilled by materials in the (GaAIB) N system.
Figure 7 shows the dispersion curves for GaN, Gao. 83Bo. 17N, A1N and Alo. osBo. 95N in the range 350-550nm. The refractive indices for GaN, GaBN and A1BN are shown by curves 70,72 and 74 respectively. The refractive index of A1N is also indicated by curve 74, as explained below. The curves for GaN and A1N are obtained from work by Yu (see G. Yu, G. Wang, H. Ishikawa, M. Umeno, T. Soga, T. Egawa, J. Watanabe, T. Jimbo, Appl. Phys. Lett. 70 (24) (1997) 3209) and Tang (see X. Tang, Y. Yuan, K.
Wongchotigul, M. G. Spencer, Appl. Phys. Lett. 70 (24) (1997) 3206) respectively. The dispersion curves for Gao. peak reflectance at 450nm (ie. blue). Curves 80,82,84 and 86 correspond to 5,10,15 and 20 periods respectively, and show an increasing value of peak reflectance. The right insert 88 shows the peak value of reflectance at 450nm versus the number of highlow refractive index ({HL}) periods, while the left insert 90 shows the change in the peak value of reflectance for a 20 period stack with resonance wavelength. A reflectance > 0. 999 at 450nm is obtained for a 25 period stack, which has a total thickness of 2.0111m, a reasonable thickness to be realised practically by epitaxial growth techniques. The peak reflectance increases with decreasing wavelength due to the increasing refractive index contrast between Gao83B0l7N and AloosBo95NX but absorption is not included in the simulation since there is no absorption data available for either compound. It is expected that absorption in Ga0. g3B0. l7N will limit the peak reflectance of such mirror stacks below 350nm.
The advantages of such mirror structures in devices such as VCSELs are as follows :i. Since the constituent layers are lattice matched, high misfit defect densities observed in GaN and A1N grown on mismatched substrates are not present.
Defect induced scattering is therefore minimised and a higher peak reflectance achieved for a lower number of mirror periods in the wavelength range discussed.
Growth times for single devices are therefore shorter, which also reduces the thickness variations in individual layers observed in nitride growth. ii. The use of Gao. 83Bo. 7N/AIo. osBo. 95N mirrors in the place of GaN/AlN mirrors allows peak reflectance values to be increased at wavelengths shorter than the absorption edge of GaN.
Figure 9 is a schematic representation of a full (GaAIBIn) N VCSEL 100. Figure 9a shows the simulated reflectance spectrum for the structure of Figure 9. The device designed consists of a lower 20 period Gao. s3Bol7N/Alo. o5BossN reflector 101, a 1), Gao. 83Bo. i7N cavity 102 with a strained GaBo tpN/GaInoN QW active region 104 designed to lase at 400nm and an upper 19 period Ga083B0. l7N/Al0o5Bo95N reflector 106. In this case the GaBN spacers 102 do not function as waveguides. A slightly lower reflectance upper mirror will define the output aperture of the device, thus avoiding absorption in the SiC substrate (SiC bandgap = 2.86eV at 300K). The VCSEL therefore emits perpendicularly to the active layer 104 through the upper reflector 106.
Double Heterostructure and QW Light Emitting Diode (LED) structures lattice matched to SiC are also possible using (GaAlB) N alloys, using similar structures to those of Figures 4a to 9.
A continuous range of materials with bandgaps from 4.30eV to 6.32eV lattice matched to 6H-SiC, can also be achieved using quaternary compounds of the form Ga, x yAlyBxN. These materials can be used to optimise the bandgap differences, band offsets (that is, how the bandgaps are aligned relative to each other) etc. in the embodiments of device structures described above. It should be noted, however that since the phase diagram of the (GaAlB) N has only been investigated for boron concentrations < 0.1, miscibility gaps may exist in certain composition ranges.
In addition to optoelectronic device applications, m-v nitrides have been extensively investigated for use in high temperature electronic devices. The materials have the advantages of low intrinsic carrier concentrations and high breakdown fields, which make them suitable for low power electronics operating at elevated temperatures. See M. Asif Khan, Q. Chen, C. J. Sun, J. W. Yang, M. S. Shur, H. Park, Appl. Phys. Lett. 68 (1996) 514; and S. C. Binari, H. B. Dietrich,'GaN and Related materials'Ed. S. J.
Pearton, Vol. 2. Ch. 16. Devices demonstrated to date include GaN/AlGaN heterostructure field effect transistors (HFETs) (see M. A. Khan, J. N. Kuznia, D. T.
Olsen, W. Schaff, J. Burn, M. S. Shur, Appl. Phys. Lett. 65 (1994) 1121), GaN/metal/semiconductor field effect transistors (MISFETs) (see S. Binari, L. B.
Rowland, W. Kruppa, G. Kelner, K. Doverspike, D. K. Gatskill, Electron. Lett. 30, (1994) 1248), and GaN/SiC heterobipolar transistors (HBTs) (see J. I. Pankove, M.
Leksono, S. S. Chang, C. Walker B. Van Zeghbroeck, MRS Journal of Nitride Semiconductor Research Vol. 1, article 39).
A reduction of the misfit dislocation density in nitride/SiC hybrid electronic devices can be achieved with use of lattice matched GaBN in the place of GaN layers. As an example, Figure 10 shows a GaBN/SiC high temperature HBT structure that is an improvement on the structure demonstrated by Pankove et al. See J. I. Pankove, US.
Patent No. 4985742 and also the Pankove reference given above.
This transistor 110 comprises a GaBN emitter 112, SiC base 114, SiC collector 116, and metal contacts 118.
The larger bandgap of the Gao. 83Bo. 17N emitter improves the high temperature operation of the transistor by increasing the valence band barrier to hole flow from the p-SiC base into the emitter. An increased device lifetime can be expected as a direct result of the reduction in the misfit dislocation density in the emitter.
In a similar manner other electronic devices can be improved by replacing mismatched AlGaN, GaN and InGaN layers by lattice matched GaBN or AIBN layers.
The devices described in all previous embodiments can be grown in a variety of ways, including expitaxially by Molecular Beam Epitaxy (MBE), (i. e. Solid Source MBE, Gase Source MBE and Metal Organic MBE (MOMBE)), or Metal Organic Vapour Phase Epitaxy (MOVPE).
Furthermore, ternary and quaternary (GaAlB) N can also be lattice matched to substrates other than 6H-SiC, including (0001) sapphire, GaN, MgA1204, ZnO, and 4H SiC, and so the growth of strain free devices on these substrates is feasible.

Claims (17)

  1. CLAIMS: 1 A semiconductor device comprising a SiC layer and at least one further layer grown, directly or indirectly on the SiC layer, wherein said further layer is a ternary or quaternary composition of the (GaInAIB) N system, comprises boron, and is substantially lattice matched to the SiC layer.
  2. 2 A semiconductor device as claimed in claim 1, which is a separate confinement heterostructure (SCH) laser diode.
  3. 3 A semiconductor device as claimed in claim 2, which comprises an active layer formed from alternating layers of GaN and GaBN.
  4. 4 A semiconductor device as claimed in claim 2, which comprises an active layer formed from alternating layers of GaBN and GaInN.
  5. 5 A semiconductor device as claimed in any one of claims 2 to 4, which further comprises a waveguide layer formed from GaBN.
  6. 6 A semiconductor device as claimed in any one of claims 2 to 5, which further comprises a cladding layer formed from A1BN.
  7. 7 A semiconductor device as claimed in any one of claims 2 to 6, wherein the SiC layer forms the substrate of the laser diode.
  8. 8 A semiconductor device as claimed in claim 1, which is a surface emitting laser.
  9. 9 A semiconductor device as claimed in claim 8, which further comprises a first reflector formed from alternating layers of GaBN and A1BN.
  10. 10 A semiconductor device as claimed in claim claim 8 or 9, which further comprises a second reflector formed from alternating layers of GaBN and A1BN.
  11. 11 A semiconductor device as claimed in claims 9 and 10, wherein said first reflector contains more alternating layers of GaBN and AIBN than said second reflector.
  12. 12 A semiconductor device as claimed in any one of claims 8 to 11, which further comprises an active layer formed from alternating layers of GaInN and GaBN.
  13. 13 A semiconductor device as claimed in claim 12, wherein said active layer is sandwiched between two spacer layers formed from GaBN.
  14. 14 A semiconductor device as claimed in any one of claims 8 to 13, wherein the SiC layer forms the substrate of the surface emitting laser.
  15. 15 A semiconductor device as claimed in claim 1, which is a light emitting diode.
  16. 16 A semiconductor device as claimed in claim 1, which is an electronic device, such as a transistor.
  17. 17 A semiconductor device as claimed in claim 16, which is a Heterobipolar Transistor (HBT), a Heterojunction Field Effect Transistor (HFET), a Metal-Semiconductor Field Effect Transistor (MESFET), a Metal-Insulator-Semiconductor Field Effect Transistor (MISFET), or a Modulation Doped Field Effect Transistor (MODFET)
GB9823778A 1998-10-31 1998-10-31 Lattice-matched semiconductor devices Withdrawn GB2343294A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB9823778A GB2343294A (en) 1998-10-31 1998-10-31 Lattice-matched semiconductor devices

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB9823778A GB2343294A (en) 1998-10-31 1998-10-31 Lattice-matched semiconductor devices

Publications (2)

Publication Number Publication Date
GB9823778D0 GB9823778D0 (en) 1998-12-23
GB2343294A true GB2343294A (en) 2000-05-03

Family

ID=10841570

Family Applications (1)

Application Number Title Priority Date Filing Date
GB9823778A Withdrawn GB2343294A (en) 1998-10-31 1998-10-31 Lattice-matched semiconductor devices

Country Status (1)

Country Link
GB (1) GB2343294A (en)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2002037579A2 (en) * 2000-11-03 2002-05-10 Cree, Inc. Group iii nitride light emitting devices with gallium-free layers
WO2005067468A2 (en) * 2003-12-19 2005-07-28 Zhaoyang Fan Iii-nitridie quantum-well field effect transistors
US7518305B2 (en) 2004-11-01 2009-04-14 The Regents Of The University Of California Interdigitated multi-pixel arrays for the fabrication of light-emitting devices with very low series-resistances and improved heat-sinking
WO2009118244A1 (en) * 2008-03-25 2009-10-01 Picogiga International Method for manufacturing a layer of gallium nitride or gallium and aluminum nitride
WO2011115529A1 (en) * 2010-03-15 2011-09-22 Yuri Georgievich Shreter Light-emitting device with heterophase boundaries

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0377940A2 (en) * 1989-01-13 1990-07-18 Kabushiki Kaisha Toshiba Compound semiconductor material and semiconductor element using the same and method of manufacturing the semiconductor element
US5005057A (en) * 1989-04-28 1991-04-02 Kabushiki Kaisha Toshiba Semiconductor light-emitting diode and method of manufacturing the same
JPH04267376A (en) * 1991-02-22 1992-09-22 Toshiba Corp Semiconductor light emitting element and fabrication thereof
WO1996019834A2 (en) * 1994-12-22 1996-06-27 Abb Research Ltd. Semiconductor device having an insulated gate

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0377940A2 (en) * 1989-01-13 1990-07-18 Kabushiki Kaisha Toshiba Compound semiconductor material and semiconductor element using the same and method of manufacturing the semiconductor element
US5005057A (en) * 1989-04-28 1991-04-02 Kabushiki Kaisha Toshiba Semiconductor light-emitting diode and method of manufacturing the same
JPH04267376A (en) * 1991-02-22 1992-09-22 Toshiba Corp Semiconductor light emitting element and fabrication thereof
WO1996019834A2 (en) * 1994-12-22 1996-06-27 Abb Research Ltd. Semiconductor device having an insulated gate

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
Patent Abstracts of Japan, Vol 17, No 57 [E-1315] & JP 04 267 376 A *

Cited By (21)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN100355093C (en) * 2000-11-03 2007-12-12 克里公司 Group III nitride light emitting devices with gallium-free layers
WO2002037579A3 (en) * 2000-11-03 2002-07-18 Cree Inc Group iii nitride light emitting devices with gallium-free layers
US6534797B1 (en) 2000-11-03 2003-03-18 Cree, Inc. Group III nitride light emitting devices with gallium-free layers
US6717185B2 (en) 2000-11-03 2004-04-06 Cree, Inc. Light emitting devices with Group III nitride contact layer and superlattice
US6784461B2 (en) 2000-11-03 2004-08-31 Cree, Inc. Group III nitride light emitting devices with progressively graded layers
WO2002037579A2 (en) * 2000-11-03 2002-05-10 Cree, Inc. Group iii nitride light emitting devices with gallium-free layers
WO2005067468A3 (en) * 2003-12-19 2005-09-15 Zhaoyang Fan Iii-nitridie quantum-well field effect transistors
WO2005067468A2 (en) * 2003-12-19 2005-07-28 Zhaoyang Fan Iii-nitridie quantum-well field effect transistors
US8796912B2 (en) 2004-11-01 2014-08-05 The Regents Of The University Of California Interdigitated multiple pixel arrays of light-emitting devices
US7518305B2 (en) 2004-11-01 2009-04-14 The Regents Of The University Of California Interdigitated multi-pixel arrays for the fabrication of light-emitting devices with very low series-resistances and improved heat-sinking
US9263423B2 (en) 2004-11-01 2016-02-16 The Regents Of The University Of California Interdigitated multiple pixel arrays of light-emitting devices
US7911126B2 (en) 2004-11-01 2011-03-22 The Regents Of The University Of California Interdigitated multiple pixel arrays of light-emitting devices
US9076711B2 (en) 2004-11-01 2015-07-07 The Regents Of The University Of California Interdigitated multiple pixel arrays of light-emitting devices
US8922110B2 (en) 2004-11-01 2014-12-30 The Regents Of The University Of California Interdigitated multiple pixel arrays of light-emitting devices
US8274206B2 (en) 2004-11-01 2012-09-25 The Regents Of The University Of California Interdigitated multiple pixel arrays of light-emitting devices
FR2929445A1 (en) * 2008-03-25 2009-10-02 Picogiga Internat Soc Par Acti PROCESS FOR PRODUCING A GALLIUM NITRIDE LAYER OR GALLIUM NITRIDE AND ALUMINUM
US8283673B2 (en) 2008-03-25 2012-10-09 Soitec Method for manufacturing a layer of gallium nitride or gallium and aluminum nitride
US8093077B2 (en) 2008-03-25 2012-01-10 S.O.I.Tec Silicon On Insulator Technologies Method for manufacturing a layer of gallium nitride or gallium and aluminum nitride
WO2009118244A1 (en) * 2008-03-25 2009-10-01 Picogiga International Method for manufacturing a layer of gallium nitride or gallium and aluminum nitride
US8901600B2 (en) 2010-03-15 2014-12-02 Yuri Georgievich Shreter Light-emitting device with heterophase boundaries
WO2011115529A1 (en) * 2010-03-15 2011-09-22 Yuri Georgievich Shreter Light-emitting device with heterophase boundaries

Also Published As

Publication number Publication date
GB9823778D0 (en) 1998-12-23

Similar Documents

Publication Publication Date Title
EP1116282B1 (en) VERTICAL GEOMETRY InGaN LED
Denbaars Gallium-nitride-based materials for blue to ultraviolet optoelectronics devices
US6533874B1 (en) GaN-based devices using thick (Ga, Al, In)N base layers
JP3644191B2 (en) Semiconductor element
US8174042B2 (en) Method of growing semiconductor heterostructures based on gallium nitride
USRE41310E1 (en) Methods for growing semiconductors and devices thereof the alloy semiconductor gainnas
US20020110947A1 (en) Semiconductor light emitting element and its manufacturing method
EP2192623A1 (en) Vertical Geometry InGaN LED
US20120100650A1 (en) Vicinal semipolar iii-nitride substrates to compensate tilt of relaxed hetero-epitaxial layers
US20070138489A1 (en) Semiconductor light-emitting device and a method of fabricating the same
JPH0864910A (en) Semiconductor light emitting element
GB2343294A (en) Lattice-matched semiconductor devices
JP3371830B2 (en) Nitride semiconductor light emitting device
JP4862855B2 (en) Semiconductor element
Bedair et al. A new GaAsP—InGaAs strained-layer super-lattice light-emitting diode
Keller Gallium nitride based materials and their application for light emitting devices
EP1115145A1 (en) Method for forming compound semiconductor layer and compound semiconductor device
JP4137042B2 (en) Semiconductor element
Matsuoka Nitride semiconductors for blue lasers
JP2001028473A (en) Growth method of n-type nitride semiconductor
KR100272127B1 (en) Semiconductor laser device
JP4069949B2 (en) Semiconductor element
JP2000077714A (en) Iii nitride semiconductor light-emitting element
JP2003347231A (en) Method of manufacturing compound semiconductor and semiconductor element
Matsuoka et al. Mysterious Material InN in Nitride Semiconductors-What's the Bandgap Energy and its Application?

Legal Events

Date Code Title Description
WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)