EP0901697A2 - Laser a semi-conducteur - Google Patents

Laser a semi-conducteur

Info

Publication number
EP0901697A2
EP0901697A2 EP97923262A EP97923262A EP0901697A2 EP 0901697 A2 EP0901697 A2 EP 0901697A2 EP 97923262 A EP97923262 A EP 97923262A EP 97923262 A EP97923262 A EP 97923262A EP 0901697 A2 EP0901697 A2 EP 0901697A2
Authority
EP
European Patent Office
Prior art keywords
layer
semiconductor laser
laser according
active layer
nitride
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.)
Ceased
Application number
EP97923262A
Other languages
German (de)
English (en)
Other versions
EP0901697A3 (fr
Inventor
Gregory Jason Dr. Parker
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.)
Parker Gregory Jason Dr
Original Assignee
BTG International Ltd
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 BTG International Ltd filed Critical BTG International Ltd
Publication of EP0901697A2 publication Critical patent/EP0901697A2/fr
Publication of EP0901697A3 publication Critical patent/EP0901697A3/fr
Ceased legal-status Critical Current

Links

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
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
    • H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
    • H01S5/18386—Details of the emission surface for influencing the near- or far-field, e.g. a grating on the surface
    • 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
    • H01S5/10—Construction or shape of the optical resonator, e.g. extended or external cavity, coupled cavities, bent-guide, varying width, thickness or composition of the active region
    • H01S5/18—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities
    • H01S5/183—Surface-emitting [SE] lasers, e.g. having both horizontal and vertical cavities having only vertical cavities, e.g. vertical cavity surface-emitting lasers [VCSEL]
    • H01S5/18386—Details of the emission surface for influencing the near- or far-field, e.g. a grating on the surface
    • H01S5/18391—Aperiodic structuring to influence the near- or far-field distribution
    • 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
    • H01S5/04—Processes or apparatus for excitation, e.g. pumping, e.g. by electron beams
    • H01S5/041—Optical pumping
    • 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
    • H01S5/3004—Structure or shape of the active region; Materials used for the active region employing a field effect structure for inducing charge-carriers, e.g. FET
    • H01S5/3009—MIS or MOS conffigurations
    • 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

  • This invention relates to a semiconductor laser.
  • Semiconductor lasers require a direct band gap material in which recombination of electron-hole pairs promotes photon emission. Photons of a particular wavelength are emitted. Two important factors govern the selection of direct band gap semiconductor materials suitable for lasers. Firstly the lattice matching of materials, from which the layers of the laser are made, is important. Secondly, is the choice of materials which determine the energy of the photon of energy emitted upon electron-hole pair recombination and this in turn determines the colour of light emitted by the laser or LED.
  • Zinc Telluride Zinc Telluride
  • ZnSe zinc selenide
  • CdTe cadmium telluride
  • a problem has been to create a p-n junction capable of supplying sufficient electrons and holes (minority carriers) to create a population inversion so that lasing can occur.
  • the doping autocompensation mechanism prevents one from trying to dope the semiconductor to the opposite type.
  • the device was shown to operate in laboratory environments and the lifetime of the laser was very short and could not be predicted with any degree of reliability. It is known that 3-5 nitrides, such as Indium Nitride (InN) and Gallium Nitride
  • GaN gallium arsphide
  • GaN gallium arsphide
  • a problem has been to achieve sufficiently high hole injection into an active layer using these materials.
  • the high n-type doping is reported to be due to a large number of nitrogen vacancies. This is possibly true and the fact that type conversion cannot be readily achieved has been attributed to an auto-compensation mechanism as found in 2-6 materials.
  • the mechanisms which prevent type conversion are not critically important for the production of a light emitter. However, an important issue is the injection of holes into n-type doped material.
  • Gallium Nitride has been made to lase by electron injection using an electron beam.
  • Gallium Nitride is normally highly n-type doped. Such materials need to be able to be type converted, so that p-n junctions can be made. This has not proved to be a straightforward matter or one which is easily soluble. In a paper published in the Japanese Journal of Applied Physics (Vol. 28 No.
  • the present invention arose from a consideration of the above mentioned problems and with a view to producing a solid state semiconductor light emitting source, preferably able to operate through the whole of the visible spectrum and into the ultraviolet (UV) region.
  • a solid state semiconductor light emitting source preferably able to operate through the whole of the visible spectrum and into the ultraviolet (UV) region.
  • a semiconductor laser comprising a substrate layer supporting a first surface of a buffer layer, a second surface of said buffer layer contacting an active layer, said active layer being adapted to supply electrons and holes capable of recombining to produce photons, and said active layer having at least one electrical contact for the supply of minority carriers for promoting recombination so as to produce photons characterised in that the substrate layer comprises a sapphire material.
  • a reflective layer formed from a material whose gain is at least 1 /t (m " * ), (where t is the thickness of the material in metres) overlays said active layer and is arranged to provide Fresnel reflection.
  • a Schottky diode would not work. This is because the Schottky diode is a majority carrier device and does not inject minority carriers into the underlying semiconductor substrate.
  • a Metal Insulator Semiconductor (MIS) structure is capable of injecting minority carriers into an underlying optically active semiconductor layer, provided a suitable MIS device is manufactured to a high quality grade.
  • MIS Metal Insulator Semiconductor
  • the buffer layer comprises Aluminium Nitride; and the active layer comprises a 3-5 material.
  • An example of a 3-5 material is Indium Gallium Nitride (InGaN).
  • a capping layer may be provided.
  • the capping layer comprises a plurality of holes or perforations formed therein. The capping layer might form an electrical contact layer.
  • the relative thicknesses of these layers is important and may be selected such that the active layer is preferably between 0.4 to 1.0 ⁇ m thick; and the Aluminium Nitride (AIN) (buffer) layer is preferably between 0.2 - 0.5 ⁇ m thick.
  • a capping layer may be interposed between the active layer and a first metal contact, said capping layer is preferably between 0.05 to 0.15 ⁇ m thick.
  • the capping layer is preferably Aluminium Nitride (AIN).
  • the reflective layer being formed from a material having a gain of at least 1/t (m " '), where t is the thickness of the material in metres, such as Gallium Nitride
  • ITO Indium Tin Oxide
  • TO Tin Oxide
  • the present invention offers advantages in direct electrical driving and does not need an optical pump source. Accordingly the laser may have a direct, electrical pump source. However, an incoherent biasing light source may be provided for supplying a suitable means for enhancing electron-hole pair production.
  • FIG. 1 is a diagrammatical section through an embodiment of the invention
  • Figure 2 is a graph showing the relative refractive indices of layers and waveguiding properties of the structure shown in Figure 1 ;
  • Figure 3 is a sectional view of an alternative embodiment of the invention.
  • Figure 4 is a plan view of the device in Figure 3.
  • FIGS 5 to 5c illustrate different types of arrays of holes which may be fabricated.
  • a laser shown generally at 10, offers the possibility of efficient photon emission throughout the whole of the visible spectrum and into the ultraviolet (UV) region. That is at wavelengths extending from around 350 nm.
  • UV ultraviolet
  • the 10 operates by injection electroluminescence using a Metal Insulator Semiconductor and a metal insulating structure (MIS).
  • the MIS comprises a metal layer 24a, b and c, an insulating layer 22 and an active semiconductor layer 16.
  • the laser 10 also has a wide band gap semiconductor layer 16.
  • the laser 10 also fulfils the requirements of a double heterostructure formed by insulating layer 22, semiconductor layer 16 and dielectric layer
  • the double heterostructure confines both carriers and photons (not shown) in an active semiconductor layer 16 (which becomes the active layer) and thereby increases photon production efficiency.
  • a Sapphire substrate 20 with a first buffer layer of Aluminium Nitride (AIN) 18 of dielectric material is grown.
  • AIN Aluminium Nitride
  • Manufacture of a similar device is described in APPLIED PHYSICS LETTERS, 64(1 1) March 1994 at pages 1377 to 1379.
  • the device described comprised similar layers to the present invention it could not be considered as a directly electrically driven laser and the publication is only referred to for purposes of disclosing an example of a suitable method of producing an Aluminium Nitride layer on Sapphire.
  • AIN aluminium Nitride
  • 6.28 eV 6.28 eV
  • AIN is both compatible with and well lattice-matched to the direct band gap 3-5 nitride alloys.
  • a metal layer which is deposited on a surface of the insulating layer 22 can be of any suitable metal and when etched reveals electrical contacts 24a, 24b and 24c.
  • Gallium nitride is a direct band gap material with a band gap energy of 3.45 eV and Indium Nitride (InN) is also direct band gap with an energy gap of 1.95 eV.
  • the alloy mixture InGaN is miscible for all alloy compositions and is also direct band gap for all compositions.
  • an InGaN alloy system is able to lase across the visible spectrum and into the ultraviolet.
  • judicious selection of relative amounts of materials enables the output wavelength of the laser to be controlled.
  • Aluminium Nitride (AIN) buffer layer 18 has three functions. Firstly, because of its larger band gap than active layer 16 it confines both carriers and photons to the active layer 16.
  • the AIN buffer layer 18 has also been shown to be an excellent buffer layer for the growth of good quality GaN layers, as mentioned above. So that subsequently grown/desposited active layer(s) are of sufficiently good quality, the AIN layer 18 should be at least 200 nm thick, although thicker layers of order 0.5 ⁇ m have been found to produce better quality GaN layers. There is then deposited an optically active layer 16. This optically active layer 16 is around 0.4 ⁇ m to l .O ⁇ m thick.
  • a dielectric "capping" layer 22 (such as a "3-5" material e.g.
  • AIN is then deposited and this needs to be relatively thin so that only small voltages (typically 4 or 5 volts) are needed to invert the active layer surface. Thicknesses will be 100 nm or less typically. However, the capping layer 22 should be thick enough so that pinholes and other defects do not cause problems. Thus the thickness of capping layer 22 is in the region 50 - 150 nm. Finally an aluminium deposition 24 is etched to form a contact 24b of an electrode. All layers 16, 18, 20 and 22 are able to be deposited to the thicknesses shown using conventional chemical vapour deposition CVD or MOCVD techniques.
  • Figure 2 illustrates that the refractive indices of the relative layers 16 to 22 are such that photon confinement will occur within the InGaN (active layer) which is one criterion necessary for an efficient laser structure.
  • the laser 10 is now turned from reverse bias into forward bias, by reversing the bias voltage, the depletion region collapses and holes collected are injected into the underlying n-type doped direct band gap semiconductor layer 16.
  • the laser 10 is formed by layers 18 and 22 and layer 16.
  • a depletion region is in the same location as the inversion layer i.e. at the interface between layer 22 and layer 16. Photon emission also occurs at this interface. This results in photon emission at the semiconductor/dielectric interface.
  • direct band gap 3-5 nitride materials In the preferred embodiment, it will be appreciated that the same approach is applicable to all semiconductor materials in which type conversion has proved difficult or impossible.
  • the largest group of direct band gap semiconductors in this category are the 2-6 compounds. From the above it is apparent that the laser or laser LED may operate in a pulsed mode. It is conceivable that the laser could also operate in a quasi Continuous Wave (C.W) mode, provided a suitable bias light is provided. Further it will be appreciated that although reference has been made to a directly electrically pumped device it may also be optically pumped if required.
  • FIGS 3 and 4 show different views of an alternative embodiment of the laser, in which one or more holes 30 are fabricated in an overlying layer such as Indium Tin Oxide (ITO).
  • ITO Indium Tin Oxide
  • the holes 30 provide Fresnel reflection and therefore remove the need for providing separate mirrors or polished end faces.
  • FIG. 5 c shows a honeycomb array 40 formed on the surface of a laser.
  • This honeycombe array allows a large photon emission area with a very small area of (absorbing) metal contact.
  • This structure allows large areas of lasers to be fabricated. These larger area arrays can be incorporated into 1 or 2 dimensional lasers as will be appreciated by a person skilled in the art.
  • the holes 30 may be formed by wet or dry etching techniques.

Landscapes

  • Physics & Mathematics (AREA)
  • Condensed Matter Physics & Semiconductors (AREA)
  • General Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
  • Semiconductor Lasers (AREA)
  • Led Devices (AREA)

Abstract

L'invention concerne un laser à semi-conducteurs (10) constitué d'un matériau de 3-5 nitrure utilisé comme matériau laser. Un exemple de ce type de matériau est l'indium gallium nitrure. Cette invention permet de résoudre les problèmes concernant les lasers existants à large bande et à courte période et dans lesquels il n'est pas possible de doper de manière fiable les 3-5 nitrures, à la fois de type p et n, et s'appuie sur l'existence d'un intervalle interdit relativement important (6,28 eV) dans la couche tampon de nitrure d'aluminium (18). La structure atomique réticulaire de la couche de nitrure d'aluminium (18) et celle de l'indium gallium nitrure (16) sont telles que l'effet laser peut se produire dans une couche d'indium gallium nitrure (16) qui est supportée sur un substrat saphir (20). L'utilisation du nitrure d'aluminium évite l'incohérence de la structure réticulaire. Selon une réalisation préférée, des miroirs de Fresnel peuvent être incorporés dans une couche supplémentaire à trous ou perforations (30).
EP97923262A 1996-05-24 1997-05-27 Laser a semi-conducteur Ceased EP0901697A3 (fr)

Applications Claiming Priority (3)

Application Number Priority Date Filing Date Title
GBGB9610928.5A GB9610928D0 (en) 1996-05-24 1996-05-24 A semiconductor laser
GB9610928 1996-05-24
PCT/GB1997/001436 WO1997045903A2 (fr) 1996-05-24 1997-05-27 Laser a semi-conducteurs

Publications (2)

Publication Number Publication Date
EP0901697A2 true EP0901697A2 (fr) 1999-03-17
EP0901697A3 EP0901697A3 (fr) 2003-10-22

Family

ID=10794273

Family Applications (1)

Application Number Title Priority Date Filing Date
EP97923262A Ceased EP0901697A3 (fr) 1996-05-24 1997-05-27 Laser a semi-conducteur

Country Status (4)

Country Link
EP (1) EP0901697A3 (fr)
JP (1) JP2002516029A (fr)
GB (1) GB9610928D0 (fr)
WO (1) WO1997045903A2 (fr)

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US20050040386A1 (en) * 2001-02-20 2005-02-24 Fow-Sen Choa Multiple quantum well broad spectrum gain medium and method for forming same
US6944197B2 (en) 2001-06-26 2005-09-13 University Of Maryland, Baltimore County Low crosstalk optical gain medium and method for forming same
CN109038214B (zh) * 2018-07-26 2020-01-03 华中科技大学 基于超表面的垂直腔面发射激光器及其制作方法

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS56120182A (en) * 1980-02-26 1981-09-21 Nippon Telegr & Teleph Corp <Ntt> Modulation system of light pumping semiconductor laser
JPS6338271A (ja) * 1986-08-04 1988-02-18 Sharp Corp 半導体面発光素子
GB9502366D0 (en) * 1995-02-07 1995-03-29 British Tech Group A semiconductor laser

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO9745903A2 *

Also Published As

Publication number Publication date
WO1997045903A2 (fr) 1997-12-04
JP2002516029A (ja) 2002-05-28
EP0901697A3 (fr) 2003-10-22
WO1997045903A3 (fr) 2003-09-04
GB9610928D0 (en) 1996-07-31

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