Juanjuan Liu

Bi2Te3 photoconductive detectors on Si

The peculiar properties of the gapless surface states with a Dirac cone shaped energy dispersion in topological insulators (TIs) enable promising applications in photodetection with an ultra-broad band and polarization sensitivity. Since many TIs can be easily grown on silicon (Si) substrates, TIs on Si could make an alternative route for photon detection of Si photonics. We present good device performances of a Si-based single-crystal bismuth telluride (Bi2Te3) photoconductive detector. Room temperature photo responses to 1064u2009nm and 1550u2009nm light illumination were demonstrated. Linear dependences of the photocurrent on both the incident light power and the bias voltage were observed. The main device parameters including responsivity and quantum efficiency were extracted.

Influence of GaAsBi Matrix on Optical and Structural Properties of InAs Quantum Dots

InAs/GaAsBi dot-in-well structures were fabricated using gas-source molecular beam epitaxy and investigated for its optical and structural properties. GaAsBi-strained buffer layer and strain reduction layer are both effective to extend the photoluminescence (PL) emission wavelength of InAs quantum dot (QD). In addition, a remarkable PL intensity enhancement is also obtained compared with low-temperature-grown GaAs-capped InAs QD sample. The GaAsBi matrix also preserves the shape of InAs QDs and leads to increase the activation energy for nonradiative recombination process at low temperature. Lower density and larger size of InAs QDs are obtained on the GaAsBi surface compared with the QDs grown on GaAs surface.

Near-infrared GaAsBi quantum well laser diodes (Conference Presentation)

Dilute bismide is a novel class of III-V semiconductor compound possessing a number of attractive physical properties such as a large band-gap bowing effect, a large spin-orbit split band and a less temperature sensitive band-gap etc. In this talk, I will present electrically pumped near infrared GaAsBi quantum well (QW) laser diodes (LDs) grown by molecular beam epitaxy with room-temperature lasing up to 1.14 uf06dm. Epitaxial growth is carefully optimized to ensure high bismuth incorporation and high optical quality at the same time. The LDs reveal an output power over 120 mW under pulsed excitation at 300 K and can operate under CW excitation up to 273 K. They also show high performance with an internal quantum efficiency of 86% and an internal optical loss of 10 cm-1. The characteristic temperature is 79 K in the temperature range of 225-350 K and the temperature coefficient of the lasing wavelength is 0.26 nm/K at 77-350 K, much smaller than 0.35-0.40 nm/K for InGaAs and InGaAsP QW LDs. These results suggest that GaAsBi LDs are attractive candidates for uncooled near infrared lasers on GaAs.

Novel group IV nano- and micro-structures for light sources on silicon

We present our recent researches on novel group IV nano- and micro-structures for potential light sources on Si, including the tensile strained Ge quantum dots (QDs), GeSn thin films and microstructures, and Ge(Sn) nanowires. Tensile-strained Ge QDs were grown by SS-MBE, and photoluminescence was achieved. The GeSn thin films were demonstrated with Sn concentration above the bandgap transition critical point, and partially suspended GeSn microstructures were fabricated for relaxing the compressive strain.

Suspended GeSn microstructure for light source on Si

A novel suspended GeSn microstructure is demonstrated by selective etching of GeSn thin film on Ge. XRD and μ-Raman measurements show that the compressive strain in the GeSn thin film is effectively relaxed, and furthermore, unexpected tensile strain was introduced in the suspended GeSn.

Electrically pumped GaAsBi laser diodes

In this paper, we present electrically pumped GaAsBi quantum well (QW) laser diodes (LDs) grown by molecular beam epitaxy. The LDs reveal a record long lasing wavelength of 1.14 µm at 300 K and can be operated under CW excitation up to 273 K. They also show high performance with an internal quantum efficiency of 86% and an internal optical loss of 10 cm−1. The characteristic temperature is 79 K in the temperature range of 225–350 K and the temperature coefficient of the lasing wavelength is 0.26 nm/K at 77 – 350 K, much smaller than 0.35 – 0.40 nm/K for InGaAs and InGaAsP QW LDs. These results suggest that GaAsBi LDs are attractive candidates for uncooled near infrared lasers on GaAs.

Electrically injected GaAsBi/GaAs single quantum well laser diodes

We present electrically injected GaAs/GaAsBi single quantum well laser diodes (LDs) emitting at a record long wavelength of 1141 nm at room temperature grown by molecular beam epitaxy. The LDs have excellent device performances with internal quantum efficiency of 86%, internal loss of 10 cm-1 and transparency current density of 196 A/cm2. The LDs can operate under continuous-wave mode up to 273 K. The characteristic temperature are extracted to be 125 K in the temperature range of 77∼150 K, and reduced to 90 K in the range of 150∼273 K. The temperature coefficient of 0.3 nm/K is extracted in the temperature range of 77∼273 K.

Photoluminescence from tensile-strained Ge quantum dots

Summary form only given. It has been theoretically predicted that 1.9% biaxial tensile strain can convert Ge, which is compatible with Si CMOS technology, into a direct band-gap semiconductor, making it a candidate material for light sources on Si. Combining the advantage of tensile strain with quantum dot (QD), we proposed that tensile-strained QD is a new route toward light emission from Ge. In this work, we chose In0.52Al0.48As, which is lattice matched to InP, as barrier layer and grew the structure by molecular beam epitaxy (MBE). Photoluminescence (PL) was successfully achieved at room temperature.

Structural and optical properties of high Bi content GaSbBi films grown by molecular beam epitaxy

GaSb_1-xBi_x thin films with 0 ≤ x ≤ 13% were grown by molecular beam epitaxy. The Bi content, lattice expansion and crystal structure were investigated by Rutherford backscattering spectroscopy, X-ray diffraction and transmission electron microscopy. Photoluminescence spectra of the GaSb_1-xBi_x alloys with various Bi contents were studied at 77 K. The bandgap energy of GaSb_1-xBi_x is decreased effectively as Bi content increasing. The PL peak energy of the 13% Bi content GaSb_1-xBi_x is extended to 2.43 μm, indicating that GaSb_1-xBi_x alloys has potentials in mid-infrared applications.