# Degradation Characteristics and Reliability Assessment of 1310 nm VCSEL for Microwave Photonic Link
## 1 Introduction  
The vertical-cavity surface-emitting laser (VCSEL) proved to be a powerful competitor to the edge-emitting semiconductor laser owing to the circular output beam, low threshold current, low cost, high-speed modulation and easy fabrication in two-dimensional arrays [1; 2; 3; 4].These characteristics enabled it to be extensively applied to microwave photonic links, short-distance optical interconnections, laser radar and chip-scale atomic clocks [5; 6; 7; 8; 9; 10]. Nowadays, VCSELs emitting at various wavelengths are extensively researched, and some of them, such as 850 nm, 940 nm and 650 nm devices, are commercialized [11; 12; 13]. VCSELs emitting at 1310 nm have broad application prospects in microwave photonic links. Opto-electronic oscillators based on VCSELs can generate a stable microwave signal with low phase noise. With the wide application of VCSEL, the reliability requirement is becoming higher. In order to improve VCSEL's long-term stability, one has studied the degradation characteristics and reliability assessment of VCSELs. In 2003, Agilent Technologies investigated the reliability and failure mechanism of oxide VCSELs in non-hermetic environments. Three failure modes of oxide VCSELs at biased 85/85 testing are identified, and dislocation growth is the most common [14]. In the same year, [PERSON] et al. found that the aperture size is the main parameter determining the device's ESD tolerance and reveals a characteristic defect structure around the tip of the oxide layer that is responsible for the creation of dislocation networks in the active region causing the device to fail ratherrapidly [15]. In 2007, [PERSON] et al. investigated the reliability of 1550 nm VCSELs. The computed activation energy for the 1550 nm VCSEL failure mechanism was about 0.79 eV and the extrapolated median VCSEL lifetime at room temperature was about 2 \(\times\) 10\({}^{7}\) h [16]. In 2009, 850 nm VCSELs had a wearout lifetime of over 24 years with less than a 1% failure rate at 70 \({}^{\circ}\)C operating conditions [17]. In 2013, [PERSON] et al. showed the mechanism for corrosion failure in oxide aperture VCSELs. Cracks near the tip of the oxide aperture cause the line dislocations, which, in turn, cause the growth of climb dislocations (DLDs) in the active region [18]. In 2019, [PERSON] et al. presented a hypothesis attributing the location of the defects around the oxide aperture edge to current crowding in that area, which increases local electrical and thermal stress [19]. In 2021, reverse-biased emission microscopy was employed to investigate a high-power VCSEL array at a non-degraded state and after high electrical stress. It has been found that degraded arrays exhibit more intense electroluminescence in areas with faulty emitters containing dark line defects in the active area [20]. The reliability of 1310 nm VCSEL has become a common problem that manufacturers and users are concerned about and need to solve urgently. In 2003, the reliability for 1.3 micron VCSELs with InGaAsNN quantum well active layers was demonstrated, and a median life of 135 years at typical operating conditions was predicted [21]. In 2013, the reliability data of wafer-fused VCSELs was presented, and at 9 mA and 8 mA, the driving current evaluation of the time to 1% failure at 70 \({}^{\circ}\)C resulted in 18 years and 30 years, respectively [22]. There are relatively few studies on the failure mechanism and reliability of a 1310 nm VCSEL at home and abroad.  
In this paper, the long-term reliability of all monolithic 1310 nm VCSELs is investigated. High current accelerated life tests are used to evaluate the 1310 nm VCSEL reliability. Variations of the properties that depend on the operating condition are characterized, and the device's median lifetime is extrapolated.