In a modification of the basic configuration of InAs quantum-dot semiconductor lasers on (001)lnP substrate, a thin layer (typically 1 to 2 monolayer thick) of GaAs is incorporated into the active region. This modification enhances laser performance: In particular, whereas it has been necessary to cool the unmodified devices to temperatures of about 80 K in order to obtain lasing at long wavelengths, the modified devices can lase at wavelengths of about 1.7 μm or more near room temperature.
InAs quantum dots self-assemble, as a consequence of the lattice mismatch, during epitaxial deposition of InAs on ln0.53Ga0.47As/lnP. In the unmodified devices, the quantum dots as thus formed are typically nonuniform in size. Strain energy relaxation in very large quantum dots can lead to poor laser performance, especially at wavelengths near 2 μm, for which large quantum dots are needed. In the modified devices, the thin layers of GaAs added to the active regions constitute potential-energy barriers that electrons can only penetrate by quantum tunneling and thus reduce the hot carrier effects. Also, the insertion of thin GaAs layer is shown to reduce the degree of nonuniformity of sizes of the quantum dots.
In the fabrication of a batch of modified InAs quantum-dot lasers, the thin additional layer of GaAs is deposited as an interfacial layer in an InGaAs quantum well on (001) InP substrate. The device as described thus far is sandwiched between InGaAsPy waveguide layers, then further sandwiched between InP cladding layers, then further sandwiched between heavily Zn-doped (p-type) InGaAs contact layer.
Once a wafer comprising the layers described above has been formed, the wafer is processed into laser diodes by standard fabrication techniques. Results of preliminary tests of experimental modified quantum-dot lasers have been interpreted as signifying that these devices lase at wavelengths from 1.60 to about 1.74 μm. The devices were found to be capable of continuous-wave operation at temperatures up to 260 K and pulse operation (duration 1 ms, repetition rate 1 kHz) at temperatures up to 280 K. It is anticipated that future such devices containing multiple stacks of quantum dots (instead of single stacks in these experimental devices) would be able to lase, at a wavelength of 2 μm. In addition, the multiple-stack devices are expected to perform better at room temperature.
This work was done by Yueming Qiu, Rebecca Chacon, David Uhl, and Rui Yang of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com/tsp under the Physical Sciences category. NPO-40243
This Brief includes a Technical Support Package (TSP).
Adding GaAs Monolayers to InAs Quantum-Dot Lasers on (001) InP
(reference NPO-40243) is currently available for download from the TSP library.
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Overview
The document is a Technical Support Package from NASA's Jet Propulsion Laboratory, focusing on advancements in InAs quantum dot (QD) lasers on InP substrates, particularly through the addition of GaAs monolayers. The research highlights the significant improvements in laser performance achieved by incorporating a thin GaAs layer in the active region of the QD lasers.
Key findings include the demonstration of InAs QD lasers that exhibit a maximum output power exceeding 15 mW at a temperature of 80 K. These lasers operate in continuous wave (cw) mode up to 260 K and in pulsed mode (1 μs, 1 kHz) up to 280 K. Notably, the lasers show very low wavelength temperature sensitivity of 0.09 nm/K, which is comparable to the sensitivity caused by changes in the refractive index. This low sensitivity is crucial for maintaining stable laser performance across varying temperatures.
The document explains that the observed lasing occurs primarily at excited states due to the configuration of the QDs. The research suggests that using multiple stacks of QDs could enable lasing at ground states, which would be around a wavelength of 2 μm, thereby enhancing the overall performance and enabling operation at room temperature.
The inclusion of a thin GaAs layer has been shown to improve the uniformity of QD size, as evidenced by atomic force microscopy (AFM) scans. The standard deviation of QD diameters decreased from 9.1 nm (without GaAs) to 5.2 nm (with GaAs), indicating a more uniform distribution of QD sizes. This uniformity is essential for optimizing the optical properties and performance of the lasers.
The document also references two key studies that explore the effects of the GaAs interface layer on the growth and luminescence of InAs QDs, emphasizing the potential for further optimization of laser performance through material engineering.
Overall, this Technical Support Package outlines significant advancements in the field of quantum dot lasers, highlighting the benefits of GaAs monolayers in improving laser efficiency and stability, which could have broader implications for various technological and commercial applications in aerospace and beyond.
