Search

US-12627117-B2 - Surface-emitting laser with optimized DBR structure and enhanced optical confinement

US12627117B2US 12627117 B2US12627117 B2US 12627117B2US-12627117-B2

Abstract

A surface-emitting laser includes a substrate, a lower DBR layer, a cavity layer, and an upper DBR layer stacked in order. The lower DBR layer has a first DBR layer, a contact layer, and a second DBR layer. The first and second DBR layers each include alternating first and second semiconductor layers containing aluminum, with the second layers having higher aluminum composition. The second DBR layer includes 12 to 20 pairs of layers. The cavity layer includes spacer layers and a quantum well light-emitting layer, with specified aluminum compositions to optimize optical confinement. The contact layer has an aluminum composition of 0.2 or less. The second DBR layer uses n-type material; the upper DBR layer uses p-type material and an oxide confinement layer. The laser forms a mesa structure with sidewall angles between 70° and 80°. This structure enables improved optical confinement, efficient carrier injection, and enhanced laser performance.

Inventors

  • Takeshi Aoki
  • Susumu Yoshimoto

Assignees

  • SUMITOMO ELECTRIC INDUSTRIES, LTD.

Dates

Publication Date
20260512
Application Date
20200331
Priority Date
20190624

Claims (9)

  1. 1 . A surface-emitting laser comprising: a lower DBR layer, a cavity layer, and an upper DBR layer that are stacked in this order on top of a substrate, wherein the lower DBR layer has a first DBR layer, a contact layer, and a second DBR layer that are stacked in this order on top of the substrate, wherein each of the first DBR layer and the second DBR layer includes a plurality of first layers and a plurality of second layers that are alternately stacked, wherein each of the first layers and the second layers is a semiconductor layer including aluminum, wherein composition of the aluminum in each first layer is lower than composition of the aluminum in each second layer, wherein the second DBR layer includes 12 or more and 20 or fewer pairs of the first layers and the second layers, wherein the cavity layer includes a first spacer layer, a second spacer layer, a light-emitting layer, a third spacer layer, and a fourth spacer layer that are stacked in this order from the lower DBR layer, wherein each of the first spacer layer and the fourth spacer layer is an aluminum gallium arsenide layer having a composition of aluminum that is greater than or equal to 0.75 and less than or equal to 0.95, wherein each of the second spacer layer and the third spacer layer is an aluminum gallium arsenide layer having a composition of aluminum that is greater than or equal to 0.25 and less than or equal to 0.45, wherein the light-emitting layer is a quantum well light-emitting layer, wherein an optical confinement factor of the contact layer is less than or equal to 1%, and wherein an optical confinement factor of the light-emitting layer is greater than or equal to 3.14% and less than or equal to 3.18%.
  2. 2 . The surface-emitting laser according to claim 1 , wherein an optical path length from the contact layer to the cavity layer is greater than or equal to 6 times and less than or equal to 10 times an oscillation wavelength of the cavity layer.
  3. 3 . The surface-emitting laser according to claim 1 , wherein the lower DBR layer includes 30 or more pairs of the first layers and the second layers.
  4. 4 . The surface-emitting laser according to claim 3 , wherein the contact layer includes aluminum gallium arsenide and composition of the aluminum in the contact layer is less than or equal to 0.2.
  5. 5 . The surface-emitting laser according to claim 1 , wherein an optical path length of the cavity layer is less than or equal to half of an oscillation wavelength of the cavity layer.
  6. 6 . The surface-emitting laser according to claim 1 , wherein a ratio of an optical confinement factor to a thickness of the contact layer is less than or equal to 2%/μm, and wherein a ratio of an optical confinement factor of the light-emitting layer to a total thickness of well layers included in the light-emitting layer is greater than or equal to 143%/μm and less than or equal to 145%/μm.
  7. 7 . The surface-emitting laser according to claim 1 , wherein the second DBR layer includes n-type aluminum gallium arsenide, wherein the upper DBR layer includes p-type aluminum gallium arsenide and an oxide confinement layer.
  8. 8 . The surface-emitting laser according to claim 1 , wherein: the second DBR layer, the cavity layer, and the upper DBR layer form a mesa, and an angle between a side wall of the mesa and a bottom surface of the mesa is greater than or equal to 70° and less than or equal to 80°.
  9. 9 . A surface-emitting laser comprising: a lower DBR layer, a cavity layer, and an upper DBR layer that are stacked in this order on top of a substrate, wherein the lower DBR layer has a first DBR layer, a contact layer, and a second DBR layer that are stacked in this order on top of the substrate, wherein each of the first DBR layer and the second DBR layer includes a plurality of first layers and a plurality of second layers that are alternately stacked, wherein each of the first layers and the second layers is a semiconductor layer including aluminum, wherein composition of the aluminum in each first layer is lower than composition of the aluminum in each second layer, wherein the second DBR layer includes 12 or more and 20 or fewer pairs of the first layers and the second layers, wherein the cavity layer includes a first spacer layer, a second spacer layer, a light-emitting layer, a third spacer layer, and a fourth spacer layer that are stacked in this order from the lower DBR layer, wherein each of the first spacer layer and the fourth spacer layer is an aluminum gallium arsenide layer having a composition of aluminum that is greater than or equal to 0.75 and less than or equal to 0.95, wherein each of the second spacer layer and the third spacer layer is an aluminum gallium arsenide layer having a composition of aluminum that is greater than or equal to 0.25 and less than or equal to 0.45, wherein the light-emitting layer is a quantum well light-emitting layer, wherein a ratio of an optical confinement factor to a thickness of the contact layer is less than or equal to 2%/μm, and wherein a ratio of an optical confinement factor of the light-emitting layer to a total thickness of well layers included in the light-emitting layer is greater than or equal to 143%/μm and less than or equal to 145%/μm.

Description

TECHNICAL FIELD The present disclosure relates to a surface-emitting laser. The present application claims the priority based on Japanese Patent Application No. 2019-116709, filed on Jun. 24, 2019, the entire contents of which are incorporated herein by reference. BACKGROUND ART The prior art document discloses a vertical cavity surface-emitting laser (VCSEL). CITATION LIST Patent Literature PTL 1: PCT International Publication No. WO 2013/176201 A1 Non-Patent Document NPL 1: M A Bobrov et al., “Mechanism of the polarization control in intracavity-contacted VCSEL with rhomboidal oxide current aperture”, Journal of Physics: Conference Series 741 (2016) 012078 SUMMARY OF INVENTION A surface-emitting laser according to the present disclosure includes a lower DBR layer, a cavity layer, and an upper DBR layer that are stacked in this order on top of a substrate, wherein the lower DBR layer has a first DBR layer, a contact layer, and a second DBR layer that are stacked in this order on top of the substrate, wherein each of the first DBR layer and the second DBR layer includes a plurality of first layers and a plurality of second layers that are alternately stacked, wherein each of the first layers and the second layers is a semiconductor layer including aluminum, wherein a composition ratio of the aluminum of each first layer is lower than that of the aluminum of each second layer, and wherein the second DBR layer includes 12 or more and 20 or fewer pairs of the first layers and the second layers. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a cross-sectional view illustrating a surface-emitting laser according to an Embodiment 1. FIG. 2 is a cross-sectional view illustrating a surface-emitting laser according to a Comparative Example 1. FIG. 3A is a diagram illustrating a result of a simulation of a refractive index and a light intensity in Comparative Example 1. FIG. 3B is a diagram illustrating a result of a simulation of a refractive index and a light intensity in Embodiment 1. FIG. 4A is a diagram illustrating a result of a simulation of an optical confinement factor. FIG. 4B is a diagram illustrating a result of a simulation of a differential resistance. FIG. 5 is a diagram illustrating a result of a simulation of an optical confinement factor of an n-type contact layer. DESCRIPTION OF EMBODIMENTS Problems to be Solved by Present Disclosure A vertical cavity surface-emitting laser is a type of semiconductor laser. In the surface-emitting laser, a lower distributed Bragg reflector (DBR) layer, a cavity layer including a light-emitting layer, and an upper DBR layer are stacked (PTL 1 and NPL 1). A surface-emitting laser array including a plurality of surface-emitting lasers may be formed. As described in PTL 1, in order to ensure isolation between surface-emitting lasers, a semi-insulating substrate is used, a contact layer is provided in a lower DBR layer, and an electrode is provided at the contact layer. A modulation speed of the surface-emitting laser depends on an optical confinement factor and a differential resistance. The modulation speed can be increased by increasing the optical confinement factor and reducing the differential resistance. The DBR layer between the contact layer and the cavity layer is a series resistance component and causes an increase in the differential resistance of the surface-emitting laser. Although the differential resistance decreases by locating the contact layer closer to the cavity layer, light leaks from the cavity layer to the contact layer, and an optical confinement is degraded. It is therefore an object of the present disclosure to provide a surface-emitting laser that can achieve both an improvement in optical confinement and a reduction in resistance. Advantageous Effects of Present Disclosure According to the present disclosure, it is possible to achieve both the improvement in optical confinement performance and the reduction in resistance. DESCRIPTION OF EMBODIMENTS OF PRESENT DISCLOSURE First, embodiments of the present disclosure will be listed and described. An aspect of the present disclosure is (1) a surface-emitting laser including a lower DBR layer, a cavity layer, and an upper DBR layer that are stacked in this order on top of the substrate. In the surface-emitting laser, the lower DBR layer has a first DBR layer, a contact layer, and a second DBR layer that are stacked in this order on top of the substrate. Each of the first DBR layer and the second DBR layer includes a plurality of first layers and a plurality of second layers that are alternately stacked. Each of the first layers and the second layers is a semiconductor layer including aluminum. A composition ratio of the aluminum of each first layer is lower than that of the aluminum of each second layer. The second DBR layer includes 12 or more and 20 or fewer pairs of the first layers and the second layers. By providing the second DBR layer including 12 or more pairs, the contact layer is away from the