Classifications

• • 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
  • H01S5/02—Structural details or components not essential to laser action
  • H01S5/0201—Separation of the wafer into individual elements, e.g. by dicing, cleaving, etching or directly during growth
• • 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
  • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
  • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
  • H01L2224/42—Wire connectors; Manufacturing methods related thereto
  • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
  • H01L2224/48—Structure, shape, material or disposition of the wire connectors after the connecting process of an individual wire connector
  • H01L2224/484—Connecting portions
  • H01L2224/48463—Connecting portions the connecting portion on the bonding area of the semiconductor or solid-state body being a ball bond
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L2224/00—Indexing scheme for arrangements for connecting or disconnecting semiconductor or solid-state bodies and methods related thereto as covered by H01L24/00
  • H01L2224/01—Means for bonding being attached to, or being formed on, the surface to be connected, e.g. chip-to-package, die-attach, "first-level" interconnects; Manufacturing methods related thereto
  • H01L2224/42—Wire connectors; Manufacturing methods related thereto
  • H01L2224/47—Structure, shape, material or disposition of the wire connectors after the connecting process
  • H01L2224/49—Structure, shape, material or disposition of the wire connectors after the connecting process of a plurality of wire connectors
  • H01L2224/491—Disposition
  • H01L2224/4918—Disposition being disposed on at least two different sides of the body, e.g. dual array
• • 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
  • H01S5/02—Structural details or components not essential to laser action
  • H01S5/0201—Separation of the wafer into individual elements, e.g. by dicing, cleaving, etching or directly during growth
  • H01S5/0202—Cleaving
• • 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
  • H01S5/02—Structural details or components not essential to laser action
  • H01S5/0201—Separation of the wafer into individual elements, e.g. by dicing, cleaving, etching or directly during growth
  • H01S5/0203—Etching
• • 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
  • H01S5/02—Structural details or components not essential to laser action
  • H01S5/0206—Substrates, e.g. growth, shape, material, removal or bonding
  • H01S5/0213—Sapphire, quartz or diamond based substrates
• • 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

Definitions

• the present invention relates to semiconductor laser diodes and more particularly relates to semiconductor laser diodes having cleaved facets.
• LEDs light-emitting diodes
• LDs laser diodes
• Blue LDs have the potential for increasing the storage capacity of optical disks over the densities currently available in compact disk systems based on red laser diodes. Increased storage capacity will open new markets for compact disks in motion picture distribution.
• One class of blue emitting elements is based on group III-V nitride films such as GaN epilayers grown on sapphire substrates.
• group III-V nitride films such as GaN epilayers grown on sapphire substrates.
• the laser cavity is typically formed by sandwiching an active gain layer between two layers of GaN doped to form n-type and p-type semiconductors.
• the GaN layers are constructed so as to form a waveguide.
• the ends of the waveguide are mirrors that reflect the light generated in the active region back and forth.
• the mirrors are typically formed by etching the ends of the waveguide to provide the reflecting surface of the mirror.
• the techniques based on cleaving the layers, which are utilized in the analogous devices, based on zinc blende III-V compounds do not work with GaN.
• the GaN layers are typically deposited on sapphire substrates that are difficult to cleave. Even if broken by force, the sapphire, GaN buffer layer deposited on the sapphire, and the GaN forming the active layer are unified at the crystal level. Hence, it is difficult to control the cleaving operation to assure that the facets are provided in the desired planes relative to the active layer.
• etching techniques have been employed.
• the surfaces formed by the etching operation do not form perfect mirror planes. Minute irregularities develop on these surfaces which scatter the light generated in the active layer. This scattering lowers the efficiency of the device, and hence, increases the current that must be applied to achieve lazing. The additional current increases the heat generated in the device and leads to decreased reliability.
• the present invention is a method for fabricating a semiconductor laser diode and the laser diode constructed therewith.
• a laser diode according to the present invention is constructed by depositing a buffer layer on a substrate.
• a crystalline layer is then deposited on the buffer layer.
• the crystalline layer includes the waveguide for the laser.
• a portion of the buffer layer is etched from under the crystalline layer leaving a portion of the crystalline layer cantilevered over the substrate.
• the crystalline layer is then cleaved in the cantilevered portion to generate a reflecting surface for reflecting light generated in the waveguide.
• This method is well suited for GaN based laser diodes that are to be constructed on sapphire substrates.
• Figure 1 is a cross-sectional view of a laser diode.
• Figure 2 is a cross-sectional view of a laser diode illustrating the manner in which the end mirrors are normally fabricated.
• Figures 3 and 4 are cross-sectional views of the layers deposited in the first stages of the fabrication of a laser diode.
• Figures 5-8 are prospective views of a wafer at various stages in the fabrication of a laser diode according to the present invention.
• Figures 9-12 are prospective views of a wafer at various stages in the fabrication of a second embodiment of a layer diode according to the present invention.
• FIG. 1 is a cross-sectional view of a LD.
• Light is generated in the active region 7 by the recombination of holes and electrons which are introduced into the region by applying a voltage between contacts 5 and 6 which in turn creates a potential across a p-n diode formed by GaN layer 3 and 4.
• the reflecting planes 1 on the boundary of the active region form a waveguide that traps the light generated in the active region.
• the light is reflected back and forth through the active region by the reflecting planes shown at 2. With each pass, the light is amplified.
• One of the reflecting planes 2 has a reflectivity that is less than 100%. Light exits the laser through this plane as shown by the arrow in the figure.
• the reflecting planes shown at 2 must be as close to perfectly parallel mirrors as possible.
• the layered structure is grown epitaxially on a substrate 8 as shown in Figure 2. If the substrate is relatively soft, the reflecting surfaces for the ends of the waveguide can be generated by cleaving the substrate and attached layers in the direction of the arrows shown at B. Typically, a scribe is used to insert cuts in the back of the substrate, and then, the substrate is broken.
• Blue semiconductor lasers are usually fabricated on a sapphire substrate because the lattice constants of sapphire provide the closest match to lattice spacing of GaN.
• a series of GaN layers are deposited on the sapphire substrate to form the various layers that make up the laser.
• the sapphire substrate is too hard to easily break after forming the active layer.
• the present invention overcomes this difficulty by utilizing a buffer layer between the sapphire substrate and the GaN layers.
• the buffer layer material must have two properties. First, it must provide a suitable base material for depositing the GaN layers. Second, the buffer material must allow a selective etch so that a portion of the buffer layer can be removed from under GaN layers to provide a cantilevered structure that can be cleaved by conventional techniques.
• the preferred buffer layer material is aluminum nitride (A1N).
• FIG. 3 is a cross-sectional view of the layers deposited on a sapphire substrate 8 as the first step in fabricating a LD 100 according to the present invention.
• An AIN layer 9 having a thickness from 50 nm to 200 ran is deposited by metal-organic chemical vapor deposition (MOCVD) at a relatively low temperature of around 500°C.
• MOCVD metal-organic chemical vapor deposition
• AIN is preferred as the buffer material because a flat film consisting of a GaN single crystal is easily formed on an AIN layer.
• etching methods for selectively etching AIN without significantly removing GaN are well known in the art.
• a layer 10 of n-type GaN is deposited.
• the light-emitting part of the layer composed of GaN based cladding layers 11 and a GaN based active layer 12, and a p-type GaN layer 13 are deposited on AIN layer 9.
• the layers are then etched to expose the n-type contact as shown at 101. The exposed area is used to make a connection that becomes the negative terminal of the LD.
• the positive terminal is deposited on p-type layer 13.
• FIG. 5 is a perspective view of a portion of wafer on which a plurality of LDs is formed by the method of the present invention.
• the layered substrate is etched to provide access to the n-type layer as described above.
• the layered structure is then etched back to the substrate 8 using reactive ion etching to provide regions in which the waveguide protrudes.
• a typical protruding region is shown at 110.
• the AIN buffer layer 9 discussed above is shown crosshatched in the figure.
• the portion of the AIN layer under the protrusion 110 is then removed by selectively etching away the exposed AIN layer. This leaves the portion of the waveguide that was included in the protrusion cantilevered over the substrate as shown in Figure 6 at 14. Without the support of the underlying substrate, the GaN layers in the cantilevered region are easily cleaved.
• the layers may be cleaved by applying ultrasonic vibration or by striking the cantilevered region with a blade at the desired location in the direction indicated by the arrows labeled "C" in Figure 7.
• the resulting cleaved facets act as the mirrors at the ends of the cavity.
• a typical facet is shown at 15 in Figure 8, which is a perspective view of one of the LDs after the wafer has been diced to separate the individual LDs.
• the reactive ion etch utilized to form the protrusions discussed above may be eliminated if the waveguides are first diced pe ⁇ endicular to the waveguide.
• the layered structure discussed with reference to Figures 3 and 4 is again etched back to expose the n-type GaN layer 10 and the waveguides.
• the wafer is then diced pe ⁇ endicular to the direction of the waveguides as indicated by the arrow labeled D. This operation cuts the waveguides into approximately the correct lengths and exposes the AIN layer 9.
• the surfaces generated by the dicing operation are not of the quality needed for the end mirrors of the LD.
• the dicing operation exposes the AIN layer 9.
• the exposed AIN layer is then selectively etched to create the gap 14 under the GaN layers as shown in Figure 10.
• the cantilevered portion of the GaN layers over gap 14 may now be cleaved by applying a blade in the direction indicated by the arrows labeled "E" in Figure 11.
• the cleaved surface 15 provides the mirrored ends of the laser cavity.
• the individual LDs may now be separated from one another by dicing parallel to the laser cavity as shown in Figure 12.

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• Physics & Mathematics (AREA)
• Engineering & Computer Science (AREA)
• Condensed Matter Physics & Semiconductors (AREA)
• General Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Optics & Photonics (AREA)
• Manufacturing & Machinery (AREA)
• Computer Hardware Design (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Power Engineering (AREA)
• Semiconductor Lasers (AREA)
• Led Devices (AREA)

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• 1997
  • 1997-01-30 JP JP1631397A patent/JPH10215031A/ja active Pending
• 1998
  • 1998-01-27 EP EP98903741A patent/EP0956623A1/de not_active Withdrawn
  • 1998-01-27 WO PCT/US1998/001494 patent/WO1998034304A1/en not_active Application Discontinuation

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