CN-122026226-A - Epitaxial stress balance preparation process of InP-based DFB laser

CN122026226ACN 122026226 ACN122026226 ACN 122026226ACN-122026226-A

Abstract

The invention provides an epitaxial stress balance preparation process of an InP-based DFB laser, and relates to the technical field of semiconductor optoelectronic device preparation. The method comprises the steps of firstly constructing an electronic impurity strain pinning surface such as a sub-monoatomic layer on the surface of a multi-quantum well active layer through trimethyl antimony precise replacement, realizing microscopic physical blocking of a tensile stress field in an atomic scale, then, utilizing a nonlinear elastic buffer transition region to dissipate residual strain energy, precisely anchoring a distributed feedback grating groove bottom to a mechanical neutral surface, solving the problems of lattice reconstruction and shape collapse in high-temperature secondary epitaxy, and finally, carrying out self-adaptive closed-loop dynamic intervention based on in-situ optical curvature online monitoring. The invention effectively inhibits the longitudinal penetration of the mismatched dislocation, and remarkably improves the locking precision of the lasing wavelength and the long-term service reliability of the device.

Inventors

ZHOU SHAOFENG
DING LIANG
LUO JUNBO
Lv tianjian
FANG ZIXUN
HUANG LIANGJIE

Assignees

深圳市星汉激光科技股份有限公司

Dates

Publication Date: 20260512
Application Date: 20260414

Claims (8)

1. An epitaxial stress balance preparation process of an InP-based DFB laser is characterized by comprising the following steps of: Sp1, sequentially epitaxially growing an N-type indium phosphide buffer layer and a lower limiting layer on an N-type indium phosphide substrate; Sp2, epitaxially growing an InGaAsP multi-quantum well active layer on the lower limiting layer, wherein the multi-quantum well active layer is formed by alternately stacking a plurality of periods of compressive strain well layers and tensile strain barrier layers; Sp3, introducing antimony source gas to the surface of the topmost layer of the multi-quantum well active layer to perform surface atomic replacement and adsorption, so as to form an isoelectron impurity strain pinning surface with the thickness of a sub-monoatomic layer; Sp4. Epitaxially growing a nonlinear stress absorbing superlattice structure on the isoelectron impurity strain pinning surface as a stress balance layer, wherein the nonlinear stress absorbing superlattice structure is made of InGaAs phosphorus material, and the molar ratio of the internal gallium element to the indium element is continuously decreased along the epitaxial growth direction in a parabolic rule so as to construct an elastic buffer transition region with smooth stress gradient; Sp5, growing an upper limiting layer on the nonlinear stress absorption superlattice structure, etching the inside of the epitaxial layer to prepare a distributed feedback grating structure, and continuing epitaxial growth of a cover layer and a contact layer; according to the process, an isoelectron impurity strain pinning surface formed by antimony atoms and a nonlinear stress absorbing superlattice structure are introduced between a multi-quantum well active layer and an upper limiting layer, macroscopic biaxial stress accumulated by the multi-quantum well active layer is subjected to finite field and distortion neutralization on an atomic scale, and a parabolic gradient elastic buffer transition region is utilized to prevent mismatched dislocation from extending to a distributed feedback grating structure.
2. The process for preparing the epitaxial stress balance of the InP-based DFB laser as set forth in claim 1, wherein the specific method for forming the strain pinning surface of the isoelectric impurity in Sp3 is that after the final growth of the multi-quantum well active layer is finished, the introduction of an indium source and a gallium source is stopped immediately, the temperature and the pressure of a reaction chamber are kept constant, trimethylantimony gas and phosphane gas are independently introduced, part of phosphorus atoms on the surface of the epitaxial layer are replaced by using the huge atomic radius of the antimony atoms, the replacement time is strictly controlled to be in a discrete antimony atom island distribution state which is enough to form ten to thirty percent coverage rate, and an upward tensile stress field is blocked at the interface in a forced manner.
3. The process for preparing the epitaxial stress balance of the InP-based DFB laser as set forth in claim 1, wherein in the Sp4, when the nonlinear stress absorption superlattice structure is grown, the flow of the trimethylgallium is adjusted in nonlinear real time through a digital mass flow controller, so that the superlattice structure is smoothly transited from a strong tensile strain state close to one side of an active layer to a completely unstrained lattice matching state close to one side of an upper limiting layer along a parabolic track, and interface barrier peaks and high-density interface state defects caused by a step-type balance layer are eliminated.
4. The epitaxial stress balance preparation process of the InP-based DFB laser as set forth in claim 1, wherein in the step of etching the Sp5 to prepare the distributed feedback grating structure, the bottom of an etching groove of the grating is precisely controlled and stopped at the central thickness position of the nonlinear stress absorption superlattice structure, and the zero stress state at the central position is utilized to prevent lattice surface reconstruction, material migration and groove collapse of the bottom of the grating groove in the subsequent high-temperature heating process of secondary epitaxy.
5. The process for preparing the epitaxial stress balance of the InP-based DFB laser as set forth in claim 1, wherein in Sp2, pure triethyl gallium is introduced for monoatomic layer flushing in a high-low temperature alternate growth stage of switching from a compressive strain well layer to a tensile strain barrier layer, and a microscopic growth step of a previous epitaxial layer is filled up by utilizing extremely high surface mobility of gallium atoms at a high temperature, so that stress concentration and lasing wavelength broadening effects caused by local microscopic thickness unevenness are weakened.
6. The epitaxial stress balance preparation process of the InP-based DFB laser as set forth in claim 1, wherein in Sp5, before the distributed feedback grating structure is etched and the second epitaxial growth coating is performed, the epitaxial wafer with the grating structure is placed in a metal organic chemical vapor deposition reaction chamber, and high-temperature in-situ thermal desorption treatment is performed in pure phosphane atmosphere, so that the surface lattice damage layer caused by etching is subjected to atomic-level self-healing in a strain-free state, and a non-radiative recombination center caused by etching is eliminated.
7. The epitaxial stress balance preparation process of the InP-based DFB laser as set forth in claim 1, wherein the contact layer grown in Sp5 is made of highly doped InGaAs material, and a layer of InGaAs-GaP transition layer with graded composition is interposed between the cladding layer and the contact layer to stabilize the surface residual thermal elastic stress generated by abrupt lattice constant changes and prevent microcracks from occurring in the later cleavage and package reflow processes of the device.
8. The epitaxial stress balance preparation process of the InP-based DFB laser as set forth in claim 1, wherein an in-situ optical reflectivity online monitoring system is adopted in the whole epitaxial growth process, wafer curvature change signals in the growth process of each film layer are extracted in real time, when the accumulated stress curvature of the multi-quantum well active layer is monitored to be close to a critical threshold value of plastic deformation, growth of an isoelectronic impurity strain pinning surface of Sp3 is triggered in advance in a self-adaptive manner, and overall process closed-loop dynamic control of stress evolution is achieved.

Description

Epitaxial stress balance preparation process of InP-based DFB laser Technical Field The invention relates to the field of semiconductor photoelectron device manufacturing, in particular to an InP-based DFB laser epitaxial stress balance preparation process. Background The wavelength stability and monochromaticity of the distributed feedback laser as a core light source in the optical fiber communication system mainly depend on the distributed feedback grating structure inside the epitaxial layer. In material systems based on indium phosphide substrates, it is often necessary to introduce an InGaAsP multiple quantum well structure in the active region in order to obtain higher modulation bandwidths and output powers. To optimize device performance, the well layers of the multiple quantum wells are typically designed to be under compressive strain while the barrier layers are designed to be under tensile strain. The traditional stress compensation process mainly relies on the principle of macroscopic 'thickness and strain product cancellation', namely, the total accumulated stress of the multi-quantum well region is theoretically towards zero by adjusting the thickness ratio of the well layer and the barrier layer and the respective lattice mismatch degree. In addition, existing fabrication approaches also involve growing a single stress compensation layer over the active region, or employing a stepwise doping adjustment to attempt to stabilize the stress. However, as optical communication technology advances toward ultra-high speed and high reliability, existing epitaxial fabrication processes face the following deep technical challenges: The stress limiting capability is insufficient, that is, the traditional thickness compensation method can only realize macroscopic average stress neutralization and cannot block dislocation migration caused by lattice distortion on an atomic scale. When the number of epitaxial layers is increased, the locally accumulated elastic energy is extremely easy to induce misfit dislocation at a microscopic interface, so that the non-radiative recombination center of the device is increased, and the service life is shortened. Thermodynamic instability of grating interface in the preparation of distributed feedback laser, it is necessary to etch the grating on the epitaxial layer and perform a secondary epitaxial coverage. The prior art does not provide an absolute "stress neutral plane" at the grating etched surface. In the high temperature rising process of the secondary epitaxy, residual interface stress can lead to surface migration and reconstruction of atoms at the bottom of the grating groove, and the grating deformation is caused, so that serious drift of the lasing wavelength is caused. The limitation of linear gradient compensation is that conventional linear graded layers or step layers still have small abrupt changes in elastic modulus at the interface, which can generate nonlinear thermal stress concentrations when the device is subjected to thermal shock, resulting in micro-cracks or wavelength chirp effects in the epitaxial layer. The existing epitaxial growth process is mostly open-loop control, and the stress balance strategy cannot be dynamically adjusted according to the real-time change of the wafer curvature in the epitaxial process, so that the stress states of different batches of products have obvious differences. Therefore, it is necessary to develop a deep epitaxy process scheme capable of realizing atomic-level strain pinning, having nonlinear stress dissipation capability, and guaranteeing physical stability of the grating structure. Disclosure of Invention Technical problem to be solved Aiming at the defects of the prior art, the invention provides an epitaxial stress balance preparation process of an InP-based DFB laser, which solves the following problems: 1. The traditional process mainly relies on adjusting the thickness proportion of the epitaxial layer to counteract macroscopic stress, and the compensation mode of the 'averaging' cannot limit distortion caused by lattice mismatch on the atomic scale. According to the invention, the isoelectron impurity strain pinning surface is introduced above the multi-quantum well active layer, and the physical obstruction formed at the interface by antimony atoms with larger atomic radius is utilized to forcibly block and limit the tensile stress field accumulated by the multi-quantum well to a specific interface like a nail, so that extension of mismatched dislocation to an upper limiting layer and a grating layer is prevented. 2. Conventional linear graded layers or stepped compensation layers still have abrupt points of elastic modulus at the interface. According to the invention, by constructing the nonlinear stress absorption superlattice structure and continuously decreasing the components of the nonlinear stress absorption superlattice structure according to a parabolic rule, the smooth dissipation of th