US-20260128571-A1 - MULTIPLE QUANTUM WELL STRUCTURE, SEMICONDUCTOR LASER AND MANUFACTURING METHOD FOR MULTIPLE QUANTUM WELL STRUCTURE

US20260128571A1US 20260128571 A1US20260128571 A1US 20260128571A1US-20260128571-A1

Abstract

An embodiment is a multiple quantum well structure between a p-type semiconductor and an n-type semiconductor in a semiconductor laser, the multiple quantum well structure including a plurality of well layers, and a plurality of barrier layers having shorter composition wavelengths than the plurality of well layers, where at least one of the plurality of well layers, excluding a p-side well layer closest to the p-type semiconductor, has a quantum level wavelength shorter than a quantum level wavelength of the p-side well layer.

Inventors

Manabu Mitsuhara
Wataru Kobayashi
Takahiko Shindo

Assignees

NIPPON TELEGRAPH AND TELEPHONE CORPORATION

Dates

Publication Date: 20260507
Application Date: 20221114

Claims (17)

1 - 8 . (canceled)
9 . A multiple quantum well structure between a p-type semiconductor and an n-type semiconductor in a semiconductor laser, the multiple quantum well structure comprising: a plurality of well layers; and a plurality of barrier layers having shorter composition wavelengths than the plurality of well layers, wherein at least one of the plurality of well layers, excluding a p-side well layer closest to the p-type semiconductor, has a quantum level wavelength shorter than a quantum level wavelength of the p-side well layer.
10 . The multiple quantum well structure according to claim 9 , wherein an interval of the quantum level wavelengths between the p-side well layer and an n-side well layer closest to the n-type semiconductor is greater than 0 nm and equal to or less than 40 nm.
11 . The multiple quantum well structure according to claim 9 , wherein compositions or layer thicknesses are different between at least one of the well layers excluding the p-side well layer and the p-side well layer.
12 . The multiple quantum well structure according to claim 9 , wherein quantum level wavelengths of the plurality of well layers become longer in order from an n-side well layer closest to the n-type semiconductor to the p-side well layer.
13 . The multiple quantum well structure according to claim 9 , wherein the plurality of well layers comprises InGaAsSb, and an Sb content of each of the plurality of well layers increases in order from an n-side well layer closest to the n-type semiconductor to the p-side well layer.
14 . A semiconductor laser comprising: the multiple quantum well structure according to claim 9 .
15 . The semiconductor laser according to claim 14 , wherein as a temperature rises, a number of holes and electrons present in an n-side well layer closest to the n-type semiconductor increases, and a gain wavelength of the entire multiple quantum well structure shifts to a shorter wavelength side as compared to a gain wavelength of a multiple quantum well structure in which quantum level wavelengths of well layers are equivalent.
16 . A manufacturing method for a multiple quantum well structure for a semiconductor laser, comprising: forming the multiple quantum well structure on an n-type InP substrate, the multiple quantum well structure including a plurality of InGaAsSb well layers and a plurality of InGaAsSb barrier layers having shorter composition wavelengths than the InGaAsSb well layers, by performing crystal growth to form the respective InGaAsSb well layers and the InGaAsSb barrier layers, alternately; and performing crystal growth of a p-type InP clad layer on the multiple quantum well structure, wherein: an amount of As supplied and an amount of Sb supplied when each of the plurality of InGaAsSb well layers is crystal-grown are equal, and an Sb content increases in order from an InGaAsSb well layer closest to the n-type InP substrate to an InGaAsSb well layer closest to the p-type InP clad layer.
17 . The multiple quantum well structure according to claim 10 , wherein compositions or layer thicknesses are different between at least one of the well layers excluding the p-side well layer and the p-side well layer.
18 . The multiple quantum well structure according to claim 9 , wherein the plurality of well layers comprise InGaAsSb, and a molar composition ratio of Sb in each well layer increases from the n-side well layer to the p-side well layer.
19 . The multiple quantum well structure according to claim 9 , wherein thicknesses of the well layers increase in order from an n-side well layer closest to the n-type semiconductor to the p-side well layer closest to the p-type semiconductor.
20 . The semiconductor laser according to claim 14 , further comprising a diffraction grating formed between a light confinement layer and the p-type semiconductor.
21 . The manufacturing method according to claim 16 , wherein crystal growth of the InGaAsSb well layers is performed with equal flow rates of gases for supplying As and Sb.
22 . The multiple quantum well structure according to claim 9 , wherein the plurality of well layers comprise InAsP, and the quantum level wavelengths of the well layers increase from 1.295 μm to 1.32 μm in order from an n-side well layer closest to the n-type semiconductor to the p-side well layer closest to the p-type semiconductor.
23 . The multiple quantum well structure according to claim 9 , wherein: the plurality of well layers comprise six InAsP well layers; the plurality of barrier layers comprise seven InGaAsP barrier layers; thicknesses of the six InAsP well layers increase stepwise from an n-side well layer closest to the n-type semiconductor to the p-side well layer closest to the p-type semiconductor; the seven InGaAsP barrier layers have identical compositions and thicknesses; and quantum level wavelengths of the six InAsP well layers increase from 1.295 μm for the n-side well layer to 1.32 μm for the p-side well layer.
24 . The semiconductor laser according to claim 14 , wherein: the semiconductor laser is a distributed feedback laser; the multiple quantum well structure is disposed between an n-type InP layer and a p-type InP clad layer; the multiple quantum well structure comprises six InAsP well layers and seven InGaAsP barrier layers; a diffraction grating is formed between an InGaAsP light confinement layer and the p-type InP clad layer; the diffraction grating has a period configured for first-order diffracted light with a wavelength of about 1.3 μm; the semiconductor laser has a ridge waveguide structure with a stripe width of 1.5 μm and a resonator length of 300 μm; one end face of the resonator has a high reflectance film and an opposite end face has a low reflectance film; thicknesses of the six InAsP well layers increase stepwise from an n-side well layer closest to the n-type InP layer to a p-side well layer closest to the p-type InP clad layer; and quantum level wavelengths of the six InAsP well layers increase from 1.295 μm for the n-side well layer to 1.32 μm for the p-side well layer.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a national phase entry of PCT Application No. PCT/JP2022/042211, filed on Nov. 14, 2022, which application is hereby incorporated herein by reference. TECHNICAL FIELD The present disclosure relates to a multiple quantum well structure. BACKGROUND In recent years, with the rapid development of services requiring large-capacity data communication, such as κG and cloud services, semiconductor lasers have been used not only for long-distance optical communication but also for short-distance optical communication in access networks or data centers. In addition, semiconductor lasers are also used as light sources for gas sensing. In gas sensing, various gases absorb light of specific wavelengths (absorption lines), and thus, by analyzing a change in light intensity when laser light is passed through a gas, a concentration of the gas and a local distribution thereof are measured in real time. A basic condition for oscillating semiconductor laser is that a gain of an active layer is greater than a loss. For this reason, in a semiconductor whose cleavage plane serves as a mirror of a resonator laser (hereinafter referred to as “Fabry-Perot laser”), a laser oscillation wavelength is near a peak wavelength of a gain of an active layer. On the other hand, an oscillation wavelength of a distributed feedback laser diode (hereinafter also referred to as “DFB laser”) that oscillates at a single wavelength is mainly determined by a period and a refractive index of a diffraction grating formed near a waveguide such as an upper portion or a lower portion of an active layer. More specifically, when first-order diffracted light is used with a period of a diffraction grating defined as Δ and a refractive index (equivalent refractive index) sensed by light propagating through a laser waveguide defined as neff, a desired oscillation wavelength λDFB in a distributed feedback laser diode is given by λDFB=2Λ×neff. It is known that an oscillation wavelength of a distributed feedback laser diode changes when an operating temperature changes, but this change in wavelength is less affected by a change in period of a diffraction grating due to thermal expansion and more affected by a change in refractive index with temperature (for example, NPL 1). As described above, a change in the oscillation wavelength of the Fabry-Perot laser with temperature depends mainly on a change in the peak wavelength of the gain. On the other hand, a change in the oscillation wavelength of the distributed feedback laser diode with temperature depends mainly on a change in the refractive index of the diffraction grating. Here, in the distributed feedback laser diode, when the oscillation wavelength is set to a wavelength having a small gain of the active layer due to a configuration of the diffraction grating, good laser characteristics (a threshold current, efficiency, and the like) cannot be obtained because of low light emission efficiency. Accordingly, in order to improve characteristics of the distributed feedback laser diode, it is necessary to set the oscillation wavelength to a wavelength having a large gain of the active layer. In this way, it is desirable to perform setting in consideration of a gain of the active layer along with a configuration of the diffraction grating. As described above, oscillation wavelengths of a Fabry-Perot laser and a distributed feedback (DFB) laser diode change with temperature at different rates (for example, NPL 1). FIG. 10 shows changes in oscillation wavelengths with temperature of a Fabry-Perot laser and a DFB laser. Active layers of the Fabry-Perot laser and the DFB laser are active layers each formed by InGaAsP on an InP substrate. A change rate of the oscillation wavelength with temperature is about 0.4 nm/K in the Fabry-Perot laser, and about 0.1 nm/K in the distribution feedback laser diode. In setting oscillation wavelengths of a Fabry-Perot laser and a distributed feedback laser diode, change rates of the oscillation wavelengths with temperature are different, and thus, it is necessary to consider a gain of an active layer at an operating temperature. For example, when an oscillation wavelength of a distributed feedback laser diode is set in accordance with a peak of a gain near room temperature, the laser can obtain good laser characteristics near room temperature, but a difference between the set wavelength and the peak of the gain of the semiconductor laser increases as a temperature difference from the room temperature increases due to the change with temperature, and thus the laser characteristics deteriorate. In order to inhibit the deterioration of the laser characteristics due to the temperature change, in general, when a semiconductor laser such as a distributed feedback laser diode is used under an environment in which an operating temperature fluctuates, the semiconductor laser is operated by installing a temperature adjusting element to k