Mengya Liao

Electrically pumped continuous-wave 1.3 mu m InAs/GaAs quantum dot lasers monolithically grown on on-axis Si (001) substrates

We report on the first electrically pumped continuous-wave (cw) InAs/GaAs quantum dot (QD) lasers monolithically grown on on-axis Si (001) substrates without any intermediate buffer layers. A 400 nm antiphase boundary (APB) free epitaxial GaAs film with a small root-mean-square (RMS) surface roughness of 0.86 nm was first deposited on a 300 mm standard industry-compatible on-axis Si (001) substrate by metal-organic chemical vapor deposition (MOCVD). The QD laser structure was then grown on this APB-free GaAs/Si (001) virtual substrate by molecular beam epitaxy (MBE). Room-temperature cw lasing at ~1.3 µm has been achieved with a threshold current density of 425 A/cm2 and single facet output power of 43 mW. Under pulsed operation, lasing operation up to 102 °C has been realized, with a threshold current density of 250 A/cm2 and single facet output power exceeding 130 mW at room temperature.

Monolithically Integrated Electrically Pumped Continuous-Wave III-V Quantum Dot Light Sources on Silicon

In this paper, we report monolithically integrated III-V quantum dot (QD) light-emitting sources on silicon substrates for silicon photonics. We describe the first practical InAs/GaAs QD lasers monolithically grown on an offcut silicon (001) substrate due to the realization of high quality III-V epilayers on silicon with low defect density, indicating that the large material dissimilarity between III-Vs and silicon is no longer a fundamental barrier limiting monolithic growth of III-V lasers on Si substrates. Although the use of offcut silicon substrates overcomes the antiphase boundary (APB) problem, it has the disadvantage of not being readily compatible with standard microelectronics fabrication, where wafers with on-axis silicon (001) substrates are used. We therefore report, to the best of our knowledge, the first electrically pumped continuous-wave (c.w.) InAs/GaAs QD lasers fabricated on on-axis GaAs/Si (001) substrates without any intermediate buffer layers. Based on the achievements described above, we move on to report the first study of post-fabrication and prototyping of various Si-based light emitting sources by utilizing the focused ion beam (FIB) technique, with the intention of expediting the progress toward large-scale and low-cost photonic integrated circuits monolithically integrated on a silicon platform. We compare two Si-based QD lasers with as-cleaved and FIB-made facets, and prove that FIB is a powerful tool to fabricate integrated lasers on silicon substrates. Using angled facet structures, which effectively reduce facet reflectivity, we demonstrate Si-based InAs/GaAs QD superluminescent light emitting diodes (SLDs) operating under c.w. conditions at room temperature for the first time. The work described represents significant advances towards the realization of a comprehensive silicon photonics technology.

Continuous wavelength operation of injection III-V microdisk lasers directly grown on Si substrate with emission wavelength beyond 1.2 µm (Conference Presentation)

A combination of high operation temperatures and small sizes of diode lasers directly grown on silicon substrates is essential for their application in future photonic integrated circuits. In this work, we report on electrically-pumped III-V microdisk lasers monolithically grown on Si substrates with active regions of two kinds: either an InGaAs/GaAs quantum well (QW) or InAs/InGaAs/GaAs quantum dots (QDs). Microdisk resonators were defined using photolithography and plasma chemical etching. The active region diameter was varied from 11 to 31 µm. Microlasers were tested without external cooling at room and elevated temperatures. The QW laser structure was epitaxially grown by MOCVD on silicon (100) with an intermediate MBE-grown Ge buffer. Under pulsed injection (0.5-µs-long injection pulses with 150 Hz repetition rate), lasing is achieved in QW microlasers with diameters of 23-31 µm with a minimal threshold current density of 28 kA/cm^2. Quasi-single mode lasing (SMSR is up to 20 dB) is observed with emission wavelength around 988 nm. To the best of our knowledge, this is the first quantum well electrically-pumped microdisk lasers monolithically deposited on (001)-oriented Si substrate. Quantum wells are typically characterized by high optical gain and high direct modulation bandwidth, which can be important in view of further miniaturization of microlasers and their future application. The sidewall passivation can be helpful to reduce the threshold current. As compared to QWs, quantum dots demonstrate reduced sensitivity to threading dislocations and other crystalline defects as well as to sidewall recombination owing to a suppressed lateral transport of charge carriers which prevents their diffusion towards non-radiate recombination centers. The QD laser structure was directly grown by MBE on Si (001) substrate with 4° offcut to the [011] plane. QD microlasers were tested at room temperature in CW regime with a DC current varied from 0 to 50 mA and at elevated temperatures under CW and pulsed excitation (0.5-µs-long injection pulses with 10 kHz repetition rate). The InAs/InGaAs QDs active region provides the wavelengths in the 1.32–1.35 µm spectral interval. At room temperature, lasing is achieved in microlasers with diameters of 14-30 µm with a minimal threshold current density of 600 A/cm2 (compare with that of 427 A/cm2 in edge-emitting laser). The threshold current density and specific thermal resistance of 0.004 °C×cm^2/mW are comparable to those of high-quality QD microdisk lasers on GaAs substrates. Lasing wavelength demonstrates low sensitivity to current-induced self-heating. Lasing is single mode (SMSR 20 dB) with a dominant mode linewidth as narrow as 30 pm. Under CW excitation lasing sustains up to 60 °C in microlasers with diameter of 30 µm. Because of self-heating, an actual temperature of the active region is close to 100°C. Under pulsed excitation, the maximal lasing temperature is 110°C. To our best knowledge, these are the smallest microlasers on silicon operating at such elevated temperatures ever reported. Up to 90°C lasing proceeds on the ground state optical transition of QDs with wavelength about 1.35 µm. At higher temperatures, lasing wavelength jumps to the excited state transition.

High-performance InAs/GaAs quantum-dot laser didoes monolithically grown on silicon for silicon photonics

III-V lasers grown on Si is the most promising solution to light sources on Si platform. The silicon-based telecommunications-wavelength III-V lasers with low threshold current density, high output power, and long lifetime will be presented.

III-IV quantum dot lasers epitaxially grown on Si

We review our recent developments, through several approaches, in the direct epitaxial growth of III-V quantum dot lasers on silicon substrates.

Integrating III-V quantum dot lasers on silicon substrates for silicon photonics

The realization of efficient III-V lasers directly grown on Si substrates is highly desirable for large-scale and low-cost silicon based optoelectronic integrated circuits. However, it has been hindered by the high threading dislocation (TD) density generated at the interface between III-V compounds and Si substrates. Introducing dislocation filter layers (DFLs) to suppress the TD propagation into the active region becomes a key factor for realising lasers with advanced performance. In this paper, optimization of InGaAs/GaAs DFLs in III-V quantum dot (QD) lasers on Si is demonstrated. Based on these optimized DFLs and other strategies, we have achieved a high performance electrically pumped QD laser on a Si substrate with threshold current density of 62.5 A cm-2, over 105 mW output power, maximum operation temperature of 120 °C and over 100,158 h of extrapolated lifetime.

Silicon-based III-V quantum dot devices for silicon photonics

Monolithically integrating III-V lasers on Si is the most promising solution to overcome the issue of lack of efficient light sources on Si platform. We demonstrated the first practical silicon-based telecommunications-wavelength InAs/GaAs quantum dot lasers with low threshold current density, high output power, high operation temperature and long lifetime.

Long lifetime quantum-dot laser monolithically grown on silicon

Monolithically integrating III-V lasers on Si is the most promising solution to overcome the lack of efficient light sources on Si platform. We demonstrated the first practical silicon-based telecommunications-wavelength InAs/GaAs quantum dot lasers with low threshold current density, high output power, and long lifetime.

InAs/GaAs quantum-dot light emitters monolithically grown on Si substrate

We report on high quality GaAs-on-Si layers with low threading dislocations obtained by a combination of nucleation layer and dislocation filter layers using the molecular beam epitaxy (MBE) growth method. As a result, we achieved a Si-based electrically pumped 1.3 μm InAs/GaAs quantum dot (QD) laser that lases up to 111°C with a lasing threshold of 200 A/cm2, and a single facet output power exceeding 100 mW at room temperature. In addition to Si-based lasers, we also demonstrated the first Si-based InAs/GaAs QD superluminescent light-emitting diode (SLD), from which a close-to-Gaussian emission with a full width at half maximum (FWHM) of ~114 nm centered at ~1258 nm and maximum output power of 2.6 mW has been achieved.