In this paper, we report a simple laser direct writing method using pulsed photoabsorption-induced disordering (PPAID) to create high spatial bandgap selectivity and high processed material quality multiple-wavelength chip in InGaAs-InGaAsP heterostructures. Using this intermixing technology, we have achieved a spatial bandgap selectively of better than 2.5mm from a two-section InGaAs-InGaAsP chip with differential wavelength shift of over 120 nm. A theoretical model has been developed to estimate the limit spatial resolution of the PPAID process. Theoretical analysis has also been performed to investigate the relationship between the irradiation conditions and the bandgap shift. Devices such as bandgap tuned lasers, integrated extended cavity lasers, and multiple-wavelength laser chip have also been fabricated and characterized to verify the integration capability of this postgrowth bandgap engineering technique. The quality of the devices fabricated from the intermixed materials was found to be high, indicating that PPAID is a promising process for the fabrication of photonic integrated circuits.
We report the performance and reliability of a 1500 nm superluminescent diode fabricated using a post-growth quantum well intermixing technique. The one-step impurity induced quantum well intermixing technique incorporating ion implantation through graded-thickness implant mask pattern is utilized here. By thermally diffusing the vacancies through the structure to the QW region, we can obtain a differential bandgap energy shift across the wafer by an amount directly related to the implant mask thickness. We use this effect to broaden the full-width half maximum of the superluminescent diode. Output powers of multiple milliwatts with full-width half maximum larger than 90 nm and spectral modulation better than 0.2 dB have been achieved from ridge waveguide multiple quantum well structure. The superluminescent diode is able to operate up to 85°C showing good uncooled operation. The true inherent superluminescent mode operation of the superluminescent diode with full-width half maximum increases along with the increment of the current injection is also discussed. Accelerated aging at continuous constant current has been carried out at 70°C, 85°C and 100°C. The life test shows a very positive result, demonstrating that this QWI technique is reliable for fabricating active devices.
In this paper, we report our research work on the application of the pulsed-laser-induced disordering (P-LID) technique in InGaAs/InGaAsP MQW waveguide photodetector. A Q-switched Nd-YAG laser with wavelength of 1.064 micrometers was used to irradiate on the InGaAs/InGaAsP quantum well materials, annealing process at 625 degree(s)C for 120s was followed. A maximum bandgap shift of up to 112meV has been observed. The variety of photocurrent curves indicated that the cut-off wavelength of the photodetector becomes shorter with increasing of intermixing strength.
N diffusion usually enhances the intermixing in GaAs/AlGaAs quantum well structure. However, Krames et al reported the reduction of layer intermixing in GaAs/AlGaAs quantum well heterostructures by an initial low-temperature 'blocking' Zn diffusion. Zn is commonly used as the dopant of the p-type GaAs substrate. To the best of our knowledge, the effect of Zn diffusion from the Zn-doped GaAs substrate on the intermixing has not been studied. In this work, we report the suppression of GaAs/AlGaAs quantum well intermixing by Zn doping in the GaAs substrate. Three samples with single GaAs/Al0.24Ga0.76As quantum wells were used in the work, all grown together by molecular beam epitaxy, but on three different substrates: Zn-doped p-type GaAs, Si-doped n-type GaAs, and semi-insulating GaAs. The samples were annealed together in a rapid thermal processor at temperatures around 900 degrees C. Photoluminescence measurements were then performed to characterize the samples. The samples with Zn-doped GaAs substrate shows more than 50 percent suppression of quantum well intermixing compared to the other two samples. It is due to Zn diffusion from the substrate into the quantum well, which induces the reduction in the number of group-III vacancies in the quantum well structure.
InGaAs/InGaAsP quantum well structures have wide applications, such as the integration of optoelectronic devices and low threshold current density laser, as well as low loss waveguides and optical switching elements. In many case, high temperature operations are necessary during the course of processing a wafer. Here, we report the influence of low and high etch pit densities (EPD) InP substrates on the thermal stability of InGaAs/InGaAsP quantum well laser structure. Both the n-type of S-doped (EPD<500 cm-2)and Sn-doped (EPD≈5x104cm-2) InP substrates were grown under the same run with half wafer each. To assess the thermal stability, the samples were annealed, using a rapid thermal processor, between 650 °C and 750 °C, for 60 seconds. 77 K photoluminescence measurements were performed on the samples after annealing to study the degree of bandgap shift. It was found that S-doped InP substrate with low EPD, i.e. low point defect density, is thermally stable up to an annealing temperature of 625 °C for 60 seconds. Compared to the S-doped materials, laser structure grown on the Sn-doped InP substrate was found to exhibit larger degree of bandgap shift resulted from defects induced quantum well intermixing.
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