FR2544133A1 - SEMICONDUCTOR DEVICE FOR GENERATING ELECTROMAGNETIC RADIATION - Google Patents

Abstract

AN ACTIVE LAYER 3 OF AN LED OR LASER IS OBTAINED WHEN IT IS EQUIPPED WITH 8 LAYERS OR ISO-ELECTRONIC WIRES. THIS AIM IS OBTAINED BY APPLYING 8 VERY THIN LAYERS OR VERY THIN THREADS (MAXIMUM THICKNESS 2 MONOMOLECULAR LAYERS) IN A MATRIX MATERIAL 7 OF A FIRST SEMICONDUCTOR MATERIAL. ESPECIALLY WHEN THE BAND SPRING OF THE SECOND MATERIAL IS LESS THAN THAT OF THE MATRIX MATERIAL, QUANTIZATION EFFECTS OCCUR IN A WAY THAT EXCITONS WITH GREAT STABILITY ARE INTRODUCED ALONG ISO-ELECTRONIC LAYERS OR WIRES.

Description

-1- "Semiconductor device used to generate radiation

6 electromagnetic 6 ticks ".

  The invention relates to a semiconductor device for

  to generate electromagnetic radiation in a semi-region

  active conductor of a first material, matrix material which

  is provided in a structured manner with a second material.

  A semiconductor device as described above is

  known from the international patent application (PCT) W 082-03946 pu-

blessed on November 11, 1982.

  Semiconductor devices used to generate electromagnetic radiation are applied in various fields of the technique They can be distinguished into devices whose radiation is not coherent and devices whose emitted radiation is coherent In the first case, it is more often LED (light emitting diode), in the last case of lasers The wavelength of the emitted radiation can be in the visible region of the spectrum, but also by

  example in the infrared or ultraviolet region.

  the radiation generated by known semiconductor lasers generally has (in the air) a wavelength of 800 to 900 nanometers For several reasons, it is desirable to achieve

  lasers emitting radiation of the shortest wavelength.

  This is how in the case of information storage in port-

  image and sound (VLP, DOR, compact disc), the amount of surface

  necessary for a single bit information is inversely proportional

  tional squared wavelength of laser radiation A

  halving this wavelength therefore allows quadru-

  pler information density A secondary advantage is that the shorter wavelengths allow the use of simpler optics. A practical realization of an LED emitting green light is known from the article entitled "An Experimental Study of High Efficiency Ga P: N Green-Light-Emitting Diodes", published in RCA Review, Vol 33, September 1972, pages 517 to 526 It describes both -2-

  LEDs where the diode is formed by mono-semiconductor material

  crystalline, for example gallium phosphide as LEDs or heterojunctions are formed between gallium phosphide and aluminum-gallium phosphide, the gallium phosphide can be

p-type as well as n-type.

  In order to increase the quantum efficiency of such TLEDs, the

  gallium phosphide is doped with nitrogen It turns out that the eff-

  quantum efficiency increases to a certain value with the amount of nitrogen impurities Too much nitrogen is

  translated however by the deformation of the network of the phosphide of gal-

  lium by formation of complexes and, as a result, a reduction in quantum efficiency In addition, the nitrogen which is farther from the

  pn junction, strongly absorbs radiation, so that the quan-

  tity of radiation actually emitted further decreases the dissolu-

  tion, a priori, in gallium phosphide, nitrogen up to the

  solubility limit therefore does not make sense.

  Said international patent application W 082-03946 describes a laser structure in which the active region consists of a relatively large number of active layers of a material

  semiconductor with direct band spacing, such as the

  gallium seniure, which are located between and separated by co-

  barrier shields of a semiconductor material having a spreader

  indirect tape like aluminum arsenide These layers

  active and these barrier layers together constitute a super-

  bucket, which has a band spacing actually located between that of Ga As (1.35 e V) and that of Al As (2.30 e V), in particular 1.57

  e V, so that the radiation generated has a wavelength

  significantly shorter than when using a cut

  active che consisting only of gallium arsenide.

  This effect is obtained by the appearance of the so-called "quan-

  tum well "and the superlattice effect The" quantum well "effect

  produced in the active region when a very thin layer of the two

  xth semiconductor material is enclosed between two layers of a first semiconductor material having a greater strip spacing than the second TI material as a result that the effective strip spacing in the thin layer of the second material increases and

2544 1 33

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  that consequently the wavelength of the radiation generated decreases

  The superlattice effect occurs as a result of the structure of

  superlattice and results in the conversion of a semiconductor material

  "indirect" content in actually "direct" semiconductor material eu

  with regard to the band transitions of the charge carriers This increases

  te the probability of the radiation transition of the carriers of

  charges, which results in a high radiation density.

  For a description of the "quantum well" effect, it should be noted

  refer to "Quantum Well Heterostructure Lasers" by N Holonyak and

  al, I E E E Journal of Quantum Electronics, Vol GE-16, N 2, fé

February 1980, pages 170 to 186.

  When making such superlattice structures where the thickness of the active layers varies between 2 nanometers and 50 nanometers and the thickness of the barrier layers between 1 nanometer and 20 nanometers, strict requirements must be placed, in particular on

the periodicity of the structure.

  The invention aims inter alia to define a semiconductor device for LEDs or lasers, where a radiation density occurs as high as possible for a current intensity

  given, especially at normal room temperature.

  In addition, it aims to define a laser of the above-mentioned struc-

  ture emitting radiation at as short a wavelength as possible. According to the invention, a semiconductor device of the kind mentioned in the preamble is characterized in that the second material is applied in the form of a wire or layer and the

  dimensions of the wire or of the layer respectively, seen in a di-

  section perpendicular to the wire or respectively to the layer, are

  at most equal to the thickness of two molecular layers of the two

  xth semiconductor material and, viewed in the longitudinal direction

  the wire or layer respectively, the dimension is equal to

  at least a hundred times the thickness of the wire or respectively of the

  che. The invention is based, among other things, on the idea that said wires or respectively said layers are thin enough to be considered as normal impurities for the material.

2544 1 33

  -4- semiconductor surrounding them, while being able to be applied in a way

  structured using modern techniques such as Spitaxis

  molecular skin (FIBE) or 1 epitaxy from the metallo-organic vapor phase. In addition, in the case where the wires or the layers respectively consist of the semiconductor material having a smaller band gap than the matrix material, it is based on the idea that there nevertheless occurs a disturbance effect in shape of quantum wells In addition, it is possible to choose materials such that this results in a good adaptation of the network The dimensions in the longitudinal direction of the wire or of the layer

  are sufficient to ensure the presence of bound states.

  The invention is then based on the idea that, in said Ga P: N structure of the above-mentioned periodical article, suitably structured layers (wires) of nitrogen atoms can be applied in the matrix material without it this results in the formation of nitrogen complexes in the matrix material proper. This object is achieved by the fact that the layers (threads) are applied to

  relatively low temperatures and no milking occurs

  subsequent thermal retention In the matrix material it does not

  therefore produces no absorption of electromagnetic radiation

generated genetics.

  In addition, a semiconductor device according to the invention

  The advantage is that stringent requirements for di-

  mensions are only applied to structured layers or wires, (thick-

  maximum of 2 molecular layers) while the structure

  is not necessarily periodic.

  According to a first embodiment, the first material

  riau and the second material consist respectively of

  aluminum arsenide and gallium arsenide A laser pre-

  feeling such an active semiconductor region emits light

red (about 630 nm) in the air.

  According to a second embodiment, the first material

  riau and the second material consist respectively of

  aluminum phosphide and gallium phosphide A laser presents

  as such an active semiconductor region emits green light

25441 3:

-5-

te (about 540 nm) in the air.

  In these two cases, there is also a good adaptation of the network of the two materials. In the said examples, the requirement concerning the thickness or respectively the section of the

  layer or wire implies that it is at most 0.6 nanometer.

  Other examples of a second material in a matrix material with greater band gap are for example: indium phosphide in gallium phosphide and arsenide

  indium or antimony gallium in gallium arsenide Or-

  Being lasers, it is possible to produce from this material also IEDs having a high light output for a

  low current intensity Then, as a result of poorer adaptation

  tation of the network, the deformation of the network results in an

  increased bond of excitons (hole-electron pairs), this

  which increases the probability of transition of electroma-

  genetic. This increase in the probability of transition by an increased bond energy of excitons also occurs when

  the second material is gallium nitride and the first material

  riau is gallium phoshure, although in this case the second

  material has a larger band gap.

  The description below, with reference to the drawings an-

  nexés, all given by way of nonlimiting example, will do well

  take how the invention can be made.

  Figure 1 shows a schematic view of a photo diode

  mettrice (LED) according to the invention.

  Figure 2 shows schematically a cross-section

  the enlarged part of the device according to Figure 1.

  Figure 3 shows a variant of Figure 2 seen along line IIIIII of Figure 4 o is shown the plan view of a

  active layer in an LED according to the invention.

  FIG. 5 schematically shows the energy levels in the active material, while FIG. 6 shows a laser according to the invention and

  FIG. 7 a variant of the device according to FIG. 6.

  The figures are represented schematically and not at -6-

  scale, and for the clarity of the drawing, in the cross-sections

  the, the dimensions in the directions of the thickness in particular

  are strongly exaggerated Generally speaking, the semi-

  of the same type of conduction are represented in a ha-

  chured in the same direction; in the figures, the corresponding parts

  are generally designated by the same reference numbers.

  rence. the light emitting diode (LED) I according to FIG. 1 comprises an n + 2 substrate of gallium arsenide, which is doped, for example using sulfur with a concentration of approximately 1018 atoms / cm 3 On this substrate is applied the active layer 3, of type n, for example by epitaxy using a molecular beam (MBE) or by epitaxy in the metallo-organic vapor phase (MOVPE) In addition, the device according to FIG. I is provided with 'an annular zone p + 4, which is for example obtained using a second epitaxy step and by pickling in the required form For the Cont Act, zone 4 is provided with a metallic layer 5 the other contact of

  diode is obtained using a metallic layer 6, ensuring the con-

tact of the substrate.

  the active layer 3 is constituted by a material of ma-

  trice 7, in this case for example of aluminum arsenide of type n, the impurities ensuring the conduction of type N being added

  during epitaxial growth to the matrix material.

  According to the invention (see Figure 2), the material

  7 is structurally provided with a second material. In this example

  ple are applied by growing layers 8 of gallium arsenide according to a thickness of a monomolecular layer of gallium arsenide (about 0.3 nanometers) In addition, the layer is at least

  a hundred times (about 30 nanometers) longer or wider In the pre-

  for example the matrix material 7 comprises several layers 8 which are spaced apart from each other by a distance of approximately 10 thicknesses of monolayer (approximately 30 nm) of the arsenide

  of gallium This substance is sufficient to ensure that disturbances

  potential states (linked states) of two different layers 8 do not

not disturb each other.

2544 1 3

-7-

  The layers 8 do not necessarily occupy all of the

  area of region 3 but can be applied as partial layers at different heights, as shown in Figure 3 o layers 8 a, 8 b, 8 c, 8 d lie in various planes and are

  partially overlap (see Figure 4).

  FIG. 5 shows a schematic energy diagram of layer 3, seen in line VV of FIG. 3 As a result of the presence of layer 8, there is a disturbance in the band structure of the matrix material 7, which has a different form than in the case of a quantum well, as indicated by the mixed line 9 In the latter case, 'several discrete energy levels

  for holes and electrons are in the quantum well, the re-

  combination of radiation being essentially present between the lowest level in the conduction band and the highest level

  high valence band of the material causing the quantum well

  that (see for example "Quantum-Well Heterostructure Lasers by N. Holonyak Jr et al, published in IEEE Journal of Quantum Electronics, Vol GE-16, N 2, February 1980, pages 170 and following, in particular pages 170 to 171) Recombination takes place at a frequency

  located between that corresponding to the strip distances of the materials

components.

  In the embodiment according to the invention (a disturbance

  tion with a layer thickness of up to two molecular layers

  laires), layer 8 is practically an office of impurity Seen in the direction along the line V-V, from the point of view of mechanics

  quantum the disturbance thus introduced can be considered as

  me a symmetrical shallow potential well, for which it can be demonstrated that only one energy level is available near the upper face of the well (see among others Landau and Lifshitz "Quantum Mechanics", second edition, Pergamon Press , 1965, pages at 67, 109 to 110, 156) The holes and electrons linked by a layer

  8 therefore occupy different energy levels

  recte respectively above the valence band and below the conduction band of the matrix material and constitute excitons linked with electrons and holes respectively The corresponding energy distance which constitutes a measure of the frequency 254413 radiated electromagnetic radiation is represented in FIG. 5 by the reference number 10 O layer 8 behaves like an "isoelectronic face", which means a layer of impurities which manifest themselves as centers of isoelectronic radiation such centers are formed by impurities having the characteristic property of binding an electron and a hole (called exciton) to a finite energy without being able

  themselves link a net charge or an electron or a hole.

  The high bond energy, in this case from

  energy levels of the symmetric potential well allows the recom-

  hoeing in the gallium arsenide layer at a frequency

  responding to an energy which is practically equal to the distance

  of energy in aluminum arsenide So it is possible to

  hold radiation of a smaller wavelength than in the

  layer 8 material itself.

  As a result of said high bond energy, the exci-

  tones also exhibit great stability which together with

  the high density, notably increases, in an isoelectric layer

  tronic, the possibility of recombination of radiation at the

  quence corresponding to said binding energy, in particular at normal ambient temperature the excitons are linked, so to speak, to the layer In, resulting in a high radiation density, the

  along the layer which is not disturbed by losses occurs

  health somewhere in the material because the radiation is essentially generated along the layer, while the arsenide

  additionally contains practically no reference centers

  combination In this example, there is also no radiation loss due to network faults because

  aluminum arsenide and gallium arsenide present practi-

  the same network constant o N 1 is the same for the

  ches or gallium phosphide wires in aluminum phosphide

  nium LEDs with such an active layer structure of-

  therefore have the advantages of a shorter wavelength

  of, of higher efficiency, while their lifespan is in

besides larger.

254413-

  -9- In the case of layers of gallium phosphide in indium phosphide or gallium arsenide in indium arsenide or in gallium-antimony, differences occur

  network constants So, recombination centers for-

  should be introduced; it is however known that in very thin layers (about 10 monomolecular layers), the network deformation can be captured elastically without causing the formation of recombination centers (see: Continuous 300 K-Laser operation of

  strained Superlattices, by Mo J Ludowise et al, Appl Phys Iett.

  42 (6), March 15, 1983, pages 487) It is true that simultaneously,

  the bonding energy of the excitons is notably increased, so

  te that these present a greater stability.

  A similar advantage is obtained in the case of the application of layers or wires of gallium nitride in gallium phosphide, in which case the matrix material has a smaller band gap than the second material, it is true, but the structured application makes it possible to obtain a higher net exciton density in gallium phosphide, in particular on faces or isoelectronic wires than according to known methods. Furthermore, because the matrix material does not itself present of unwanted recombination centers, we obtained an LED with

higher yield.

  the device according to FIG. 6 presents a semi-laser

  conductor 11 composed of a substrate 12 of gallium arsenide

  type N with high doping (Ga As) on which several layers are formed

  ches by growth using molecular beam epitaxy or

  metallo-organic vapor phase epitaxy -The substrate 12 pre-

  feels for example a thickness of 200 micrometers and is doped with the aid of approximately 5 1018 selenium atoms / cm 3 On this substrate are applied respectively a layer 13 of gallium arsenide (Ga As) with high doping of a thickness about 0.5 micrometer and doping of 3 1018 selenium atoms / cm 3, a layer 14 in

  Ga%, 8 A 10.2 As doped N-type As (about 1.5 1018 ato-

  of selenium / cm 3) with a thickness of approximately 0.5 micrometer and a layer of type N 15 of aluminum arsenide with a thickness of

  1.5 micrometer and doped with 8 1016 selenium atoms / cm 3.

  254413 z -10- Next is applied the active layer 16 with a thickness of about 50 nanometers This layer consists of a material

  of aluminum arsenide matrix, in which is / are applied

  quée (s) in a structured way one or more layers in gallilrn arsenide in a similar way to the structure of the active layer 3 of

  LED as described using figures 1 to 4.

  The laser also has a p-type layer 17 at the rear.

  1.5 micrometer thick aluminum seniure with

17 3

  doping of approximately 3 1017 atoms / cm of zinc and a layer of con-

  high doped p-type tact 18 with doping of approximately

  1.1019 atoms / cm 3 and a thickness of 0.1 micrometer.

  In addition, the laser 11 is provided with metal contacts 19 and 20 for current injection When a certain current of

  threshold is exceeded, the laser 11 will emit electromagnetic radiation

  in a direction perpendicular to the plane of the drawing.

  In the device according to FIG. 6, the width of the active region is limited to, for example, 6 micrometers by making,

  using the electrode 20 which acts as a mask, a bombard-

  proton which extends to the region bounded by the

  broken line 21 So region 16 is mostly

  due inactive and the laser effect occurs only in a narrow band.

  The same result can be obtained by removal by deca-

  page of part of the layer structure using the electrode 20 which serves as a mask In this case, a device is obtained as

  shown schematically in Figure 7, the reference figures

  this having the same meaning as in FIG. 6 In general, the cavity obtained by pickling is filled later at

  using suitable protective material.

  It is obvious that the invention is not limited to the examples

  ples described above but that several variants are possible

  for the specialist without departing from the scope of the present invention.

  This is how many other combinations of materials can

  be chosen for the active layer, for example emitting ray-

  indation having a longer wavelength For the matrix material one can choose for example indium phosphide and for -11- the layers of indium antimonide or indium arsenide De

  more, it is possible to use ternary or quater-

  Appropriately chosen naires In addition, as already mentioned

  mentioned above, it is possible to apply wire structures

instead of layer structures.

  In addition, instead of current injection, it is possible to use electron injection, for example in the case where a layer of a composition mentioned above is used in a device as described in the application. Dutch patent

  N 8300631 in the name of the Applicant.

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Claims (9)

  1 Semiconductor device used to generate rayon-   electromagnetic in an active semiconductor region of a first material, matrix material which is provided in a structured manner with a second material, characterized in that the second   material is applied in the form of a wire or layer and the dimensions   sions of the wire or the layer respectively, seen in one direction   perpendicular to the wire or respectively to the layer, are at most   mum equal to the thickness of two molecular layers of the second semiconductor material, and seen in the longitudinal direction of the wire or respectively of the layer, the dimension is equal to the   minus a hundred times the thickness of the wire or the layer respectively.   2 semiconductor device according to claim 1, charac-   terized in that the first semiconductor material has more   larger band spacing than the second material.   3- semiconductor device according to claim 2, charac-   terized in that the structure of the second semiconductor material has several wires or layers spaced apart from each other by a distance greater than the thickness of eight monomolecular layers   of the first semiconductor material.   4 semiconductor device according to claim 2, charac-   terized in that the first semiconductor material is made   with aluminum arsenide and the second semiconductor material   tor consists of gallium arsenide.   5 semiconductor device according to claim 2, charac-   terized in that the first semiconductor material consists of aluminum phosphide and the second semiconductor material   consists of gallium phosphide.   6 semiconductor device according to claim 4 or 5, characterized in that the thickness of the layer or the section of the wire is at most 0.6 nanometers.   7 semiconductor device according to claim 1, charac-   terized in that the first semiconductor material consists of gallium phosphide and the second semiconductor material   consists of gallium nitride. 2544 1 33 -13-   8 Light emitting diode according to one of the preceding claims.   teeth, characterized in that a pn emitting junction is located between the active semiconductor region having a first type of   conduction and a second semiconductor zone having two   xth type of conduction opposite to the first type of conduction.   9 Light emitting diode according to claim 8, characteristic   sée that the active layer is applied to a layer of the second type of conduction 'and the pn junction is formed more by a   region of the second type of conduction which is depressed in an an-   ring through the active layer.   Semiconductor laser according to one of Claims 1 to 7,   characterized in that the active semiconductor region is shaped   layer and is on one side between several semiconductor layers   of a first type of conduction and, on the other hand, between several semiconductor layers of a second type of conduction   which is opposed to the first type of conduction.