The researchers used a quantum dot laser on Si (001) for co-doping lift

The Semiconductor Materials Science Key Laboratory and the University of Sciences claim that indium Arsenide (InAs) quantum dot (QD) laser significantly improves performance on silicon (Si) through space separation co-doping [Shuai Wang et al., Optics Letters, v31, p20449, 2023].

The researchers attribute the improved performance to "effective passivation of non-radiative recombination centers around quantum dots by N-type direct doping" in the device's active light-producing region (Figure 1). The zone consists of five indium gallium arsenide (InGaAs) Wells separated by P-doped (beryllium) GaAs barriers. InAs quantum dots are grown in holes of doped silicon at a concentration of 4.4x1010 dots/cm 2 density.

The researchers comment on the effects of quantum dot n doping: "The carrier loss of the quantum dot laser is reduced and the mode gain is improved, especially at high injection currents and operating temperatures.

Previously, modulated p doping of the barrier in QD lasers has been found to effectively compensate for hole losses during device operation, thereby improving differential gain, temperature stability, and small-signal modulation response. However, one disadvantage is that the threshold current increases due to the higher non-radiative auger recombination rate, which negatively affects power consumption.

Doped quantum dot N-type results in lower threshold current density, higher slope efficiency, smaller line-width enhancement factor, and narrower near-field laser dots. Co-doping with P-type barriers and N-type points has been shown to reduce power consumption and improve thermal stability. The deployment of codoping techniques on silicon substrates has the potential to compensate for the reduction in the quality of the III-V epitaxial layer materials (increased defects).

The researchers comment: "This work shows great promise for co-doping techniques for enhancing the performance of silicon-based QD lasers for reduced power consumption, improved temperature stability and higher operating temperatures to facilitate the development of future low-cost and high-performance silicon photonic chips."

Laser material structure growth by solid-state molecular beam epitaxy (MBE) on gallium phosphide (GaP) on Si (001) template to avoid inverse boundary defects.

The 2700nm III-V buffer consists of a 1600nm GaAs, a 200nm dislocation filter (DFL) and a 900nm GaAs spacer. The DFL consists of ten superlattice strain layers (10nm In0.14 Canadian 0.86As/10nm GaAs). Cyclic annealing improves the crystal structure. The thread dislocation density is estimated to be as low as 8.7x106/ cm 2.

The waveguide layer is gallium arsenide, and the cladding is aluminum gallium arsenide (Al0.4 and 0.6 as the language).

The reference material is grown without n doping of the quantum dots. The doping concentration is about 1x1018/ cm 3. For barrier P-type doping, this corresponds to about 13.6 holes/points; It is estimated that for smaller volume points, doping produces about 1.6 electrons/points.

Standard 6μmx1mm ridge waveguide laser diode (LD) was prepared from the epitaxial material. The cracked surfaces are coated with a 97% reflective dielectric stack 2/Ta2O5 layer composed of silica and tantalum pentoxide (SiO).

The p+n co-doped QD laser achieves a threshold current of 28.1mA (468A/cm) 2) for continuous wave (CW) operation at room temperature (25°C). Only the p diode has a 40.3mA (672A/cm) 2) threshold. Other reported PQD-only semiconductor laser tubes have reached a threshold as low as 266A/cm 2, suggesting room for improvement and optimization.

The maximum power output of the codoped semiconductor laser tube reaches 69mW, while only the p device reaches 55mW. The saturation currents are 375mA and 335mA, respectively. The slope efficiency of both devices is approximately 27.200W/A at 0mA injection current.

The ground state laser wavelengths of n+p and p doped semiconductor laser tubes are 1305nm (40mA) and 1296nm (50mA), respectively.

The thermal performance of laser diodes is evaluated at pulse modes between 15°C and 115°C. At the highest temperature, the threshold for codoped devices is 102mA, while the threshold for P-only semiconductor laser tubes is 267mA. The maximum power output of the co-doped diode is 115mW at 8°C. The threshold is characterized by temperature (T0), 15-85°C, 102K and 87K for codoped and P-only devices, respectively. The corresponding characteristics (T1) of slope efficiency are 556K and 513K at 15-55°C, respectively.

The researchers report that the n+p semiconductor laser tube maintains a ground-state laser at 2mA continuous operation at 1342°C, with a peak wavelength of about 175.115nm (Figure 2), adding: "To the best of our knowledge, this result is better than the highest continuous operating temperature reported to date for P-doped individual QD lasers grown on Si (108) at 001°C, and close to the best value C for 119° scrap silicon (incompatible CMOS)."

The team expects to improve by optimizing material quality, doping concentration, equipment process and packaging technology.

Source: Laser Network