FR2804794A1 - METHOD FOR SELECTIVELY CONTROLLING THE OXIDATION OF A LAYER IN A VERTICAL CAVITY SURFACE EMISSION LASER, AND LASER OBTAINED BY MEANS OF THIS METHOD - Google Patents

Abstract

A method for controlling the oxidation of a layer (190) containing oxidizable material that extends in a transverse plane of a vertical cavity surface emitting laser denoted VCSEL is disclosed, further comprising a substrate (101), Bragg stacks (109) and (127), an active region (117) and a contact region (132). The method performs selective ion implantation in transversely separated regions of the layer (190) to modify the concentration of oxidizable material in the transversely separated regions. Next, the layer is oxidized, the degree of oxidation of the layer varying in the transverse direction between the implanted regions (190a) and the non-implanted regions (190b) of the layer. The invention also relates to the laser thus produced.

Description

The present invention relates generally to lasers with emission in

  surface with vertical cavity, noted VCSEL, and, more particularly, a process

  allowing to control the selective oxidation of VCSELs.

  In a VCSEL, an active region is arranged between stacks of layers with alternating refractive indices which form Bragg mirrors in a vertical arrangement. Typically, Bragg layers are made

  gallium arsenide / gallium aluminum arsenide (GaAs / AlGaAs).

  VCSELs are advantageous for a number of reasons, such as their planar structure, the fact that they emit light perpendicular to the surface of the chip, and the possibilities they offer for group manufacturing. They find for example their applications as

  excitation devices in fiber optic communications.

  In a complete VCSEL, regions of optical confinement are arranged on either side of the active region. Transition regions are placed between the optical confinement regions and the Bragg mirrors so as to allow the smooth transition from the optical confinement region to the Bragg stacks. Contact regions are formed on the outside of the Bragg stacks. The transition regions are typically formed from layers of AlAs or AlGaAs to ensure adaptation with the layers of

Bragg.

  A typical VCSEL of this type is described in U.S. Patent No. 5,764,671, which may be referred to for further

further information.

  It is desirable to selectively oxidize parts of the AlAs or AlGaAs layers of Bragg mirrors or transition regions so as to obtain a certain number of advantages such as better confinement of the carriers, reduced series resistance, etc. ., which improves the optical gain and lowers the threshold current of the VCSEL. This technique is described in U.S. Patent No. 5,359,618, which may be

report.

  In the prior art, the oxidation process is controlled by varying the time or the flow of water vapor, which means, in practice, that the sample is removed from the oven or that the cut is simply cut. arrival of water vapor. It is also known in the prior art that the percentage of gallium can be modified to reinforce or reduce the oxidation of the

layer of massive Al (x) Ga {x) As.

  An object of the invention is to improve the ability to carry out oxidation

  selective of parts of the Bragg layers.

  According to the invention, there is provided a method for controlling the oxidation of a layer containing an oxidizable material extending along a transverse plane in a surface emission laser with vertical cavity (VCSEL), the method comprising the operations following: selectively implanting ions in regions transversely separated from the layer in order to modify the concentration of oxidizable material in the regions transversely separated, then oxidizing the layer, so that the degree of oxidation of the layer in a transverse direction varies between established regions and regions not

layer implanted.

  For example, the implantation of Ga ions in AlAs or AlGaAs will lower the AI concentration, which will then have the effect of significantly reducing the oxidation rate. By masking the layer, we can selectively

  control the oxidation speed on its transverse dimension.

  Other types of ions can be used to control oxidation in a particular layer. For example, the implantation of oxygen ions can be used to effect the selective oxidation of a layer having a high concentration of Al. In this case, the wafer must be heated after

implantation.

  This technique can be applied to all materials for VCSEL in which a change in the metal concentration (normally A1)

  in a particular layer is desired.

  By making more reproducible components, production efficiency can be increased, giving consumers a

better quality product.

  The invention also provides a surface emission laser with a vertical cavity, comprising at least one oxidation layer which contains an oxidized material divided into a plurality of transversely separated regions where ions have been implanted, the degree of oxidation of said ion. layer varying in the transverse direction between said implanted regions and said non-implanted regions of

said layer.

  We will now describe the invention in a little detail, by way of example, with reference to the single figure, this being a section

right made in a VCSEL.

  The VCSEL 10 is formed on a substrate 101 which has a region of

  touch on its reverse side. The VCSEL 10 consists of a stack of Bragg 109.

  of an active region 117, which can be sandwiched between optical confinement layers of a Bragg stack 127 and of a contact region 132. This general structure is described in more detail in the United States patent. United States of America No. 5,764,671, to which reference may be made if desired. A layer 190 intended for oxidation and consisting of AlGaAs is placed above the active layer 117. The oxidation layer 190 is provided for oxidation and aims to improve the properties of the device such as

described above.

  During the manufacturing process, layer 190 is masked to leave exposed regions 190a while regions 190b are covered with the mask. Gallium ions are then implanted, using a conventional implantation process, into the exposed regions 190a to reduce

  the Al concentration in layer 109.

  After removing the mask from the oxidation layer 190, the device is placed in an oxidation oven, in a conventional manner. The degree of oxidation varies on the wafer in the direction indicated by the arrow X. Where the concentration of Ai is reduced, in region 190a, there is a significant decrease in the speed of oxidation, which results in the degree

  oxidation varies over the extent of the wafer.

  By varying the size of the regions 190a and the implantation dose, we

  can selectively control, over the range of the wafer, the degree of oxidation.

Claims (10)

  1. Method for controlling the oxidation of a layer containing an oxidizable material which extends along a transverse plane in a surface emission laser with vertical cavity (denoted VCSEL), characterized in that it comprises the following operations : selectively implanting ions in regions transversely separated from said layer in order to modify the concentration of oxidizable material in said regions transversely separated, then oxidizing said layer, so that the degree of oxidation of said layer in a transverse direction varies between implanted regions and   non-implanted regions of said layer.   2. Method according to claim 1, characterized in that said layer is made of AlAs or AlGaAs, the aluminum constituting said oxidizable material. and   said ions are gallium ions.   3. Method according to claim 1, characterized in that said layer contains Al, which forms said oxidizable material, and said ions are oxygen ions. 4. Method according to claim 1, characterized in that the said heating is heated layer after implantation.   5. Method according to any one of claims 1 to 3, characterized in that   that said ion implantation is carried out in said regions through a mask.   6. Method according to any one of claims 1 to 5, characterized in that   that the implantation dose of said transversely separated regions varies over the extent of the layer.   7. Method according to any one of claims 1 to 6, characterized in that   that the size of said transversely separated regions varies over the extent of the layer. 8. Surface emission laser with vertical cavity. characterized in that it comprises at least one oxidation layer (190) containing an oxidized material which is divided into a plurality of transversely separated regions (190a, 190b) in which ions have been implanted, the degree of oxidation of said layer (190) varying in the transverse direction between said implanted regions   (190a) and said non-implanted regions (190b) of said layer.   9. vertical cavity surface emission laser according to claim 8, characterized in that said layer is made of AlAs or AlGaAs, and said ions are gallium ions.   10. Surface emission laser with vertical cavity according to claim 8, characterized in that said oxidizable material is aluminum and said ions.   implanted are oxygen ions.