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
  • H01L33/10—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
  • 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
  • H01L33/44—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 coatings, e.g. passivation layer or anti-reflective coating
  • H01L33/46—Reflective coating, e.g. dielectric Bragg reflector
  • H01L33/465—Reflective coating, e.g. dielectric Bragg reflector with a resonant cavity structure

Definitions

• the invention relates to a light-emitting diode according to the preamble of patent claim 1.
• a DBR mirror distributed Bragg Reflection
• a DBR mirror contains a plurality of layer pairs of epitaxially produced semiconductor layers which differ in their refractive index and their optical thickness, ie the product of the refractive index of the respective layer with the layer thickness, in each case one quarter of the wavelength of the radiation emitted by the light-emitting diode equivalent.
• the chip surface provided for radiation decoupling also has a certain reflectivity due to the refractive index difference from the surrounding medium, which may be a potting compound, in particular an epoxy resin, so that in cooperation with the chip surface DBR mirror a resonator arises.
• This resonator can cause unwanted resonances in the emission spectrum of the light-emitting diode.
• the resonance effect can even lead to the emission spectrum of the light-emitting diode having a plurality of intensity maxima at different wavelengths and / or emission angles. This has a particularly disturbing effect on applications of light-emitting diodes in optical measuring methods.
• window layers serve both for current spreading and for light extraction. Due to the thickness of the layers, the resonances are spectrally so close to each other that they usually do not interfere in applications. Such layers are also often not planar, either as a result of certain processing steps or due to the layer growth itself, which also counteracts the resonances. However, the growth of such is thicker Layers associated with a high production cost and therefore high costs.
• the invention has for its object to provide a light emitting diode, are reduced in the resonances in the emission spectrum with a relatively low production cost.
• the reflection-reducing layer sequence according to the invention comprises a DBR mirror formed from at least one layer pair. Mirror in the main beam direction subsequent annealing layer, and disposed between the DBR mirror and the annealing layer intermediate layer.
• the reflectivity of the layers arranged above the active zone is reduced such that unwanted resonances in the emission spectrum of the light-emitting diode are largely avoided.
• the residual reflectivity of the reflection-reducing layer sequence depends in particular on the number of layer pairs of the DBR mirror. It has proved to be advantageous if this is formed from between one and including ten pairs of layers, more preferably between and including one and including four pairs of layers.
• the optical thickness of the intermediate layer is preferably equal to half the wavelength of the emitted radiation. Furthermore, it is advantageous if the optical thickness of the tempering layer is equal to an odd multiple of a quarter of the wavelength ⁇ of the emitted radiation, that is, for example, 1/4 ⁇ , 3/4 ⁇ or 5/4 ⁇ . With these layer thicknesses, a particularly good antireflection coating can be achieved.
• the intermediate layer is preferably a semiconductor layer and can be grown epitaxially with advantageously low production costs directly on the semiconductor layers of the DBR mirror.
• the tempering layer is, for example, a dielectric layer and may in particular contain a silicon oxide or a silicon nitride.
• a radiation-transmissive conductive oxide (TCO-transparent conductive oxide), in particular ZnO, is also suitable.
• the tempering layer can be doped, for example with aluminum. This is advantageous in particular when partial areas of the tempering layer are provided with electrical contacts, since in this case the tempering layer can simultaneously act as a current spreading layer.
• An Al-doped ZnO layer is particularly suitable for this purpose.
• the tempering layer may also form an ohmic contact with the underlying intermediate layer.
• the light-emitting diode is preferably embedded in a potting compound, for example an epoxy resin.
• the potting compound may also contain a luminescence conversion material in order to shift the wavelength of the radiation emitted by the luminescence diode longer wavelengths.
• Suitable luminescence conversion materials such as YAG: CE (Y 3 Al 5 O 2 : Ce 3+ ), are described, for example, in WO 98/12757, the contents of which are hereby incorporated by reference.
• the reflection-reducing layer sequence according to the invention for light-emitting diodes in which a second mirror, in particular a second DBR mirror, is arranged between a substrate and the active zone.
• a second mirror in particular a second DBR mirror
• the radiation emitted by the light-emitting diode into the substrate is prevented from penetrating into the substrate by the second mirror, whereby the risk of the occurrence of undesired resonances in the substrate is at the same time prevented by the reflection-reducing layer sequence
• the effect of the reflection-reducing layer sequence according to the invention is independent of the distance of the reflection-reducing layer sequence to the second mirror and / or the active zone.
• the invention is not limited to light-emitting diodes having a substrate and a second mirror applied thereto.
• the light-emitting diode may also comprise a so-called thin-film semiconductor body, in which an epitaxial layer sequence grown on a growth substrate has been separated from the growth substrate and mounted on a carrier body.
• thin-film semiconductor bodies contain on the side facing the carrier body a reflective layer, which can also form a resonator with the opposite surface, which is generally provided for radiation decoupling.
• the total thickness of the reflection-reducing layer sequence is advantageously less than 2000 nm.
• FIG. 1 shows a schematic representation of a cross section through an exemplary embodiment of a light-emitting diode according to the invention
• FIG. 2 shows a graph of the reflectivity R of a reflection-reducing layer sequence as a function of the wavelength ⁇ for different numbers of layer pairs of the DBR mirror when using a SiN-tempering layer,
• FIG. 3 shows a graph of the reflectivity R of a reflection-reducing layer sequence as a function of FIG Wavelength ⁇ for different numbers of layer pairs of the DBR mirror when using a ZnO-coating layer
• FIG. 4 shows a graph of the intensity I of the emitted radiation as a function of the wavelength ⁇ without consideration of reflection losses, when using a conventional antireflection coating and when using a reflection-reducing layer sequence according to the invention with a SiN coating,
• FIG. 5 shows a graph of the intensity I of the emitted radiation as a function of the wavelength ⁇ without consideration of reflection losses, when using a conventional antireflection coating and when using a reflection-reducing layer sequence according to the invention with a ZnO coating, and
• Figure 6 is a schematic representation of a cross section through a light emitting diode according to the prior art.
• the state-of-the-art luminescence diode 17 shown in FIG. 6 includes a substrate 2 and a DBR mirror 5 applied to the substrate 2 and formed of a plurality of layer pairs of the epitaxially deposited semiconductor layers 3 and 4.
• the DBR mirror 5 reflects back radiation emitted in the direction of the substrate 2.
• the light-emitting diode contains a radiation-emitting active zone 7, which is arranged between cladding layers 6, 8 and emits radiation in a main radiation direction 15.
• the light-emitting diode 17 is embedded in a potting compound 10. In order to reduce reflection losses at the interface between the semiconductor material and the potting compound 10, a coating layer 9 is provided.
• a resonator can be produced by the residual reflectivity at the boundary surfaces between the tempering layer 9 and the potting compound 10 and / or the interface between the potting compound 10 and a surrounding medium, for example air, in conjunction with the DBR mirror 5, whereby unwanted Resonances in the emission spectrum of the LED can occur.
• the light-emitting diode 1 according to the invention shown in FIG. 1 contains a substrate 2, which may be, for example, a GaAs substrate.
• a layer pair can each have an Al 0 . 5 Ga 0 . 5 As layer 3 and an Al 0 . 95 Ga 0 .0 5 AS layer 4 included.
• the number of layer pairs of the DBR mirror 5 is about 20, for example.
• the DBR mirror 5 reflects back radiation emitted in the direction of the substrate 2. In this way, the intensity of the radiation emitted in the main radiation direction 15 is increased and absorption losses in the substrate 2 are reduced.
• the luminescence diode 1 contains a radiation-emitting active zone 7.
• This can be, for example, an approximately 0.2 ⁇ m thick layer of Ini- ⁇ Ga x Al y P with O ⁇ x ⁇ l, O ⁇ y ⁇ l and x + y ⁇ l included to one Emission wavelength of about 600 nm to achieve.
• the active zone may also contain other semiconductor materials and have a different emission wavelength.
• the active region 7 is arranged, for example, between a p-type cladding layer 6 and an n-type cladding layer 8, each having a thickness of about 0.8 ⁇ m.
• the light-emitting diode 1 may for example be embedded in a potting compound 10, in particular an epoxy resin.
• the luminescence diode 1 contains a reflection-reducing layer sequence 16.
• the reflection-reducing layer sequence 16 contains a DBR mirror 13 following the active zone 7 in the main beam direction 15, which is formed from one or more layer pairs.
• the DBR mirror 13 is advantageously made of epitaxially grown semiconductor layers 11, 12 whose optical thickness corresponds to one quarter of the wavelength of the emitted radiation.
• the DBR mirror 13 may be made of at least one pair of layers each of an Alo.sGao.sAs semiconductor layer 11 and an Alo.gsGao.osAs semiconductor layer 12.
• the reflection-reducing layer sequence 16 contains a compensation layer 9 adjoining the potting compound whose optical thickness likewise preferably corresponds to one quarter of the wavelength of the emitted radiation, or alternatively to another odd-numbered multiple of the wavelengths ⁇ such as 3/4 ⁇ or 5/4 ⁇ .
• the tempering layer may in particular contain a silicon nitride, a silicon oxide or a zinc oxide.
• the reflection-reducing layer sequence 16 contains an intermediate layer 14, for example Alo. 5 Gao. Contains 5 As and has an optical thickness that corresponds to about half the wavelength of the emitted radiation.
• the reflection-reducing layer sequence forms in this way a reflection-reducing resonator.
• the reduction of the reflection by the reflection-reducing layer sequence 16 according to the invention depends decisively on the number of layer pairs of the DBR mirror 13. This is illustrated in the following simulation of the reflectivity of the layers arranged above the active zone 7.
• FIG. 2 shows a simulation of the reflectivity R of a reflection-reducing layer sequence as a function of the wavelength ⁇ for different numbers of layer pairs of the DBR mirror.
• the reflectivity R was simulated as a function of the wavelength ⁇ without a DBR mirror (curve 18), for a DBR mirror 13 with a layer pair (curve 19), with two layer pairs (curve 20) and with three layer pairs (curve 21). , The optimal antireflection is thus achieved with a DBR mirror 13, which contains only one pair of layers.
• the reflectivity of the arranged above the active zone 7 layers was without DBR mirror (curve 22), with a DBR mirror with a pair of layers (curve 23), with two pairs of layers (curve 24), with three pairs of layers (curve 25) and four pairs of layers (curve 26) simulated.
• the simulation calculations make clear that in this case the best antireflection with a DBR mirror 13 with two layer pairs is achieved.
• the DBR mirror 13 In general, similar to a symmetrical Fabry-Perot resonator, the DBR mirror 13 must have approximately the same reflectivity as an outer reflector which is formed from the layer transitions between the intermediate layer 14 and the tempering layer 9 and between the tempering layer and the potting compound 10, to minimize the residual reflectivity. For this reason is at the
• Embodiment with a coating layer 9 of ZnO compared to the embodiment with a coating layer of SiN required an additional layer pair. Since ZnO has a lower refractive index than SiN, the refractive index difference of the temper layer 9 to the adjacent intermediate layer 14 is larger, thereby increasing the reflectivity of the outer reflector. Due to the additional layer pair in the DBR mirror 13, an adaptation of the reflectivity of the DBR mirror 13 to the outer reflector is achieved in this case.
• the DBR mirror 13 may also include layers 11, 12 whose optical thicknesses deviate from ⁇ / 4.
• the thickness of the layer 11 could, for example, 1.2 ⁇ / 4 and the thickness of the layer 12 0.8 ⁇ / 4 be.
• the reflectivity of the DBR mirror 13 can be adapted to the reflectivity of the outer reflector.
• Refractive index difference of the layers 11,12 of the DBR mirror 13 are varied in order to achieve an optimum anti-reflection. This is possible, for example, with AlGaAs semiconductor layers by varying the Al content.
• FIG. 4 shows a simulation of the intensity I of the emission (in arbitrary units) for a light-emitting diode with a SiN coating. While the emission spectrum without a DBR mirror 13 according to the invention (curve 27) is clearly influenced by resonances, the emission spectrum of a light-emitting diode with a reflection-reducing layer sequence according to the invention, which is shown in curve 28, differs only insignificantly from the emission spectrum shown in curve 29 no external reflections were considered.
• the effect of the reflection-reducing layer sequence 16 according to the invention in the emission spectra of a luminescence diode shown in FIG. 5 with a coating layer 9 made of ZnO is even more apparent. While the emission spectrum simulated in the curve 30 has two maxima without a reflection-reducing layer sequence 16 according to the invention, the emission spectrum simulated in the curve 31 with a reflection-reducing layer sequence 16 according to the invention has a similar course to the emission spectrum of the active zone 7 simulated in the curve 32 without consideration of the outside influences.
• the reflection-reducing layer sequence 16 according to the invention is particularly advantageous because twice or even multiple maxima in the emission spectrum when using a light emitting diode in precise optical measurement methods prove very disturbing, especially in measuring methods in which differential signals are detected, for example in temperature or thermal resistance measurement.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Computer Hardware Design (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Power Engineering (AREA)
• Led Devices (AREA)

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• 2004
  • 2004-08-24 DE DE102004040968A patent/DE102004040968A1/de not_active Withdrawn
• 2005
  • 2005-06-15 WO PCT/DE2005/001065 patent/WO2006012818A2/de active Application Filing
  • 2005-06-15 US US11/659,066 patent/US20080224156A1/en not_active Abandoned
  • 2005-06-15 KR KR1020077004555A patent/KR101145541B1/ko not_active IP Right Cessation
  • 2005-06-15 JP JP2007522905A patent/JP2008508697A/ja not_active Withdrawn
  • 2005-06-15 EP EP05760046A patent/EP1771890A2/de not_active Withdrawn
  • 2005-07-28 TW TW094125523A patent/TWI305692B/zh not_active IP Right Cessation

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