FR2887373A1 - OPTOELECTRONIC COMPONENT COMPRISING A SEMICONDUCTOR OPTICAL GUIDE WITH AN ENHANCED OPTICAL INDEX ACTIVE HEART - Google Patents

Abstract

The invention relates to an optoelectonic component comprising a semiconductor optical guide comprising an active core comprising a quantum well structure (MPQ, MPQ1, MPQ2) based on AlxlnyGazN, with x, y, z mole fractions between 0 and 1, inserted between ohmic contact layers, on the surface of a substrate (S), characterized in that the active core further comprises at least one layer of high optical index (CF, CF1, CF2) in a first material indium-based semiconductor, said index being higher than that of said structure and in that it comprises optical confinement layers (CO1, CO2, CO) made from a second semiconductor material with high mobility n-doped GaN or n-doped AIGaN type electrodes, said optical confinement layers being the ohmic contact layers.Applications: Modulator operating at several hundred GHz

Description

OPTOELECTRONIC COMPONENT COMPRISING A GUIDE

  OPTICAL SEMICONDUCTOR WITH AN ACTIVE INDEX HEART

REINFORCED OPTICS

  The field of the invention is that of optoelectronic components that may be of the type: optical transmission devices comprising at least one emission laser section, photodiodes or electro-optical modulators in semiconductor material, with quantum wells involving inter-subband transitions.

  This type of modulator is very attractive for applications requiring a bandwidth of up to several hundred GHz. Indeed, carrier relaxation in sub-bands may be more than 100 times faster than that between the valence and conduction bands. It is possible to design modulation or detection at the wavelengths used in fiber optic telecommunications with a GaN III-V material system. In this case, a multi-electron-volt conduction band discontinuity of the quantum well active material made from GaN / AlN or InGaN / AlGaN layers which has electronic levels separated by the near-infrared transition energy IR is exploited. . The corresponding radiation can be modulated or detected thanks to the electro-absorbing effect according to the absence or the presence of the carriers (electrons) on the fundamental level.

  In order to be able to exploit the intrinsic speed of the transition for modulation with an electrical signal, the device must have very low parasitic resistance and capacitance. A light guide structure, similar to those used in conventional III-V modulators or in the lateral photodiodes, is known to optimize the electroabsorbent effects with respect to parasitic capacitance. It also has the advantage of being able to control the polarization of the radiation relative to the quantum well plane.

  However, the design of a guide in GaN-AIN close to the mesh agreement and presenting the low optical losses presents a difficulty because of the very close optical indices due to the energy of the radiation very far from the gap of all the materials of the guide. An additional difficulty to solve is the electrical access to the active material with very low product (resistance x capacity). In particular, obtaining a low resistance limits the choice of material, especially for wide-gap semiconductors close to dielectric insulators. By way of example, the GaN / AlN active material has the index of 2.1, while the conductive material making it possible to produce ohmic contact layers in n-doped GaN, has an index of 2.3.

  The case of GaN / AIN is not limiting. A similar difficulty may exist in other families of materials for other applications.

  Furthermore, it is necessary to design architectures comprising both optical confinement layers to delimit a guiding structure and ohmic contact layers for electrically controlling the modulator-type structure. According to a conventional approach, it is necessary to search for a confinement material with a lower index than that of the heart in GaN / AlN quantum wells.

  A first possibility is to use AIN (index of 2.00) as a confinement layer positioned between the n-GaN layer on which ohmic contact is made and the active zone. The diagram of the component is shown in FIG. 1. On a substrate S, the stack of semiconductor layers is produced according to: a first contact layer Ohmic Cri a first confinement layer Coi an active emission zone Za a second layer of confinement Col a second Cc2 ohmic contact layer The lateral confinement is ensured thanks to the realization of a mesa within the layers Coi, Za, Co2 and Cc2 The problem of such a device is the difficulty of carrying out a doping n and the very low electron mobility in AIN (300cm2V-s') which does not allow to achieve a low resistance electrical access between the ohmic contact on n-GaN and the active zone. We find the same situation if the insulating AIN material is replaced by any transparent dielectric such as SiO2 or Si3N4. In the case of a modulator, this type of device could still work but with the disadvantage of very high control voltages, due to the electric field distributed over a thickness 10 to 20 times higher than that of the active layer.

  A second possibility is always to use AIN (or a transparent dielectric) as a confinement layer. On the other hand, the n-GaN contact layer is positioned between the AlN confinement layer and the active zone. The diagram of the component is shown in FIG. 2. On a substrate S, the stack of semiconductor layers is carried out according to: a first confinement layer Col a first ohmic contact layer Cc1 an active emission zone Za a second layer of ohmic contact Cc2 a second confinement layer Col The lateral confinement is ensured thanks to the realization of a mesa within the layer Col.

  The electron mobility of n-GaN is important (1000 cm 2 V -s') but the product (resistance x capacity) RC of such a device is high because, to avoid optical losses, the metallizations of the contacts (not shown) must away from the active area where the mode is contained. The estimate of the RC product indicates that this device does not allow use at very high frequencies (3dB attenuation at 10GHz).

  In this context, the present invention proposes to increase the index of the active core of the structure, to advantageously be able to use single layers to play both the role of optical confinement layer and ohmic contact layer.

  More specifically, the subject of the invention is an opto-electronic component comprising a semiconductor optical guide with an active core comprising a quantum well structure based on AIXInyGaZN, with x, y, z mole fractions between 0 and 1, inserted. between ohmic contact layers, on the surface of a substrate, characterized in that the core further comprises at least one layer of high optical index in a first semiconductor material based on indium nitride, said index being higher as that of said structure and in that it comprises optical confinement layers made from a second n-doped GaN or n-doped GaN-type semiconductor material, said optical confinement layers being the contact layers. ohmic.

  According to a first variant of the invention, the active core may comprise on both sides of the quantum well structure two layers of high index material.

  According to a second variant of the invention, the active core may comprise two quantum multiwell structures separated from each other by a layer of high index material.

  Advantageously, the high-index material may be of n-doped InN type, n-doped InGaN or else n-doped AIGaInN.

  Advantageously, the optoelectronic component according to the invention may comprise a mesa type architecture so as to confine the emission of the guide in a direction parallel to the plane of the layers.

  Advantageously, the opto-electronic component according to the invention may comprise an active core confined laterally and vertically within an ohmic contact layer, so as to produce the guide.

  The invention will be better understood and other advantages will become apparent on reading the description which follows given by way of non-limiting example and by virtue of the appended figures in which: FIG. 1 illustrates a first embodiment of an opto-electronic component with an optical guide according to the known art.

  FIG. 2 illustrates a second exemplary embodiment of an optoelectronic component with an optical guide according to the known art.

  FIG. 3 illustrates a first variant of the invention comprising a layer of high-index material integrated between two quantum well structures and comprising a mesa-type architecture. FIG. 4 illustrates a first variant of the invention comprising a layer of high-index material. high index material, integrated between two quantum well structures and comprising a laterally confined active core; FIG. 5 illustrates a second variant of the invention comprising two layers of high index material on either side of a quantum well structure and comprising a mesa type architecture; FIG. 6 illustrates a second variant of the invention comprising two layers of high index material on either side of a quantum well structure and comprising a confined active core. 7 shows simulation results for an example of an optoelectronic component with a guide according to the first variant of FIG. FIG. 8 illustrates simulation results for an example of optoelectronic component with a guide according to the second variant of the invention.

  In general, the opto-electronic component according to the invention may be a laser, a modulator, a photodiode requiring a guide.

  In the latter case, the modulation can be carried out directly on the source laser by driving its supply current or by producing an integrated component comprising, on the same substrate, a transmission laser section and a modulation section of the optical power. emitted by the laser.

  The component according to the invention can also be of the photodiode type having a high speed of reaction.

  According to the invention, by integrating into the core of the structure, a layer of high optical index, it becomes possible, contrary to the prior art, to use conventional layers of high electron mobility as optical confinement layers which generally have indices. relatively high optical More specifically it is a question of introducing layers with a high optical index in the core having the lowest index in order to keep these properties active. The new stack of layers will have the average optical index of the center of the guide greater than that of the confinement layers chosen for their good electrical conductivity.

  An example of the GaN / AIN sub-band modulator component will be described below to describe the proposed solution; Nevertheless the basic idea applies to other semiconductor materials like InGaN / AIGaN.

  One of the possible structures uses n-doped GaN or n-doped AIGaN, good conductors, as confinement and contact layers, and n-doped InN, n-doped InGaN or n-doped AIGaInN, with a subscript greater than that of the confinement layers, as constituent layers in particular. the active heart. This active core has a stronger index than that of the confinement layers and includes the weak index active zone. The interest of n-InN or n-InGaN is the high electronic mobility of these materials (3000 cm2V-1s 1).

  It is therefore possible to reduce the access resistance from the top of the structure by using for example a mesa structure and to reduce the RC for high frequency use.

  According to a first variant of the invention, a central layer CF is inserted between two quantum well structures MPQ1 and MPQ2, so as to produce the active core, after a first confinement layer Col on the surface of a substrate. S. A first practical solution is to use a high index layer for example n-doped InGaN (index of 2.70) positioned in the center with the active zone on either side (index 2.10). The diagram of the component is represented in FIG. 3 in the case of a guide whose lateral confinement is achieved thanks to a mesa architecture, within the upper confinement layer CO2.

  FIG. 4 illustrates the same variant with a buried guide architecture, in which the active core is confined laterally within a single confinement layer C. According to a second variant of the invention, the guide may comprise two layers of material with a high index CF1 and CF2, which can typically be n-InGaN (index of 2.70) positioned on either side of the quantum well structure MPQ (index of 2.10) so as to form the active core. The diagram of the component is represented in FIG. 5, in the case of a guide whose lateral confinement is achieved thanks to a mesa architecture, within the upper confinement layer CO2.

  FIG. 6 illustrates the same variant with a buried guide architecture, in which the active core is confined laterally within a single confinement layer C. Several stacking variants of the layers of the active core can be envisaged provided that I average index of said stack is greater than that of the conductive confinement layers. Simple stacks will advantageously be used to reduce the technological complexity and which optimize the confinement of the optical field in the active layer.

  In general, the active guide proposed in the optoelectronic component according to the invention has the advantage of significantly reducing the access resistance with respect to the semiconductor guides operating far from the gap and known from the state of the art. In particular, it allows the choice of confinement materials having the higher index of the index of the active-effect layer (electro-absorption, electro-optical, absorption, gain, etc.) which, in this way, can be chosen for properties of good conductivity.

  To validate the performance of the components of the invention described above and in particular their guiding structure, simulations have been carried out using an ALCOR software (Beam protocol method developed by France Telecom) based on the exemplary embodiments of FIGS. variants previously described: First embodiment: n-GaN confinement layers Active layer in quantum wells made from alternating AIN / GaN layers High-index layer on either side of n-InGaN: A plate epitaxial is constituted on Al2O3 substrate of: - 2pm of Col n-GaN confinement layer, - 0.05pm of MPQ1 active layer, - 0.20pm of high CF n-InGaN layer, 0.05pm of MPQ active layer 2 and 1 μm of Col n-GaN confinement layer.

  A ribbon structure is developed to provide lateral confinement of 0. 75pm and width of 2pm. This guide structure is monomode. This structure is modeled using the ALCOR software.

  ALCOR gives the result that the structure is monomode with an average index of 2.32 for a confinement in the active zone of 13.8%. The mode is shown in Figure 7.

  Second exemplary embodiment: n-GaN confinement layers Active multi-well quantum well layer made from alternating AIN / GaN layers High-index layer on either side of n-InGaN: An epitaxial plate is consisting of Al 2 O 3 substrate of: 2pm Col n-GaN confinement, 0.10pm of high CF1 n-InGaN layer, 0.10pm of MPQ active layer, - 0.15pm of high CF2 n-InGaN layer - and lpm of CO2 confinement layer in n-GaN.

  A ribbon structure is developed to provide lateral confinement of 0. 75pm and width of 2pm. This guide structure is monomode. This structure is modeled using the ALCOR software.

  ALCOR gives the result that the structure is monomode with an average index of 2.32 for a confinement in the active zone of 15.4%. The mode is shown in Figure 8.

  The simulations above prove the monomode operation, often sought for efficient coupling with optical fibers, and the possibility of obtaining the optical confinement factors in the active core compatible with the good functioning of the devices (> 10%).

Claims (6)

  An optoelectronic component comprising a semiconductor optical guide comprising an active core comprising a quantum well structure (MPQ, MPQ1, MPQ2) based on AIXInyGaZN, with x, y, z mole fractions between 0 and 1, inserted between ohmic contact layers, on the surface of a substrate (S), characterized in that the active core further comprises at least one layer of high optical index (CF, CF1, CF2) in a first semiconductor material based indium nitride, said index being higher than that of said structure and in that it comprises optical confinement layers (Col, CO2) made from a second semiconductor material with high electron mobility doped GaN type n or n-doped AIGaN, said optical confinement layers being the ohmic contact layers.   2. Optoelectronic component according to claim 1, characterized in that the active core comprises on either side of the quantum well structure two layers of high index material (CF1, CF2).   3. The opto-electronic component according to claim 1, characterized in that the active core comprises two quantum well structures (MPQ1, MPQ2) separated from each other by a layer of high-index material. 4. opto-electronic component according to one of claims 1 to 3, characterized in that the high index layer is of n-type material InN, InGaN or AIGaInN doped.   5. Optoelectronic component according to one of claims 1 to 4, characterized in that it comprises a mesa-type architecture so as to confine the transmission of the guide in a direction parallel to the plane of the layers.   6. opto-electronic component according to one of claims 1 to 4, characterized in that the active core is confined laterally and vertically within a confinement layer (Co), so as to achieve the guide.