Self-assembled ErAs islands in GaAs: Growth and subpicosecond carrier dynamics

Abstract

We report the growth of self-assembled ErAs islands embedded in GaAs by molecular beam epitaxy. The nucleation of ErAs on GaAs occurs in an island growth mode leading to spontaneous formation of nanometer-sized islands. Several layers of ErAs islands separated by GaAs can be stacked on top of each other to form a superlattice. X-ray diffraction shows superlattice fringes from such samples. Pump-probe measurements indicate carrier capture times as short as 120 fs. These capture times are strongly correlated with the period of the superlattice.

Quantum dot materials for terahertz generation applications

“…Differential reflection measurements on QD layers with ∼100nm vertical separation showed sub-ps carrier capture from bulk GaAs into the wetting layer and ∼1.5 ps capture time into the QDs [20]. Additionally, the periodicity of embedded QD layers has been shown to also strongly influence the carrier capture time [21].…”

Effects of nanoscale embedded Schottky barriers on carrier dynamics in ErAs:GaAs composite systems

“…Hybridized metal nanostructure/GaAs systems controlled by ultrafast optical pulses can achieve much faster switching than is attainable by phase change, voltage-driven carrier injection, liquid crystals or the modulation of superconductivity 2 . Interest in the embedded nanoparticle ErAs:GaAs composite system stems from the ability to control the optical and electronic properties of GaAs by incorporating semimetallic ErAs nanoparticles without altering the position of the GaAs bandgap 3 and retaining high quality, atomically sharp ErAs/GaAs interfaces 4,5 . The composite systems display tunable photo-carrier relaxation with ultrashort relaxation times spanning two orders of magnitude 3,6 , while achieving greater film quality 1,7-9 and transport characteristics than low temperature grown GaAs 1,10-16 .…”

“…Interest in the embedded nanoparticle ErAs:GaAs composite system stems from the ability to control the optical and electronic properties of GaAs by incorporating semimetallic ErAs nanoparticles without altering the position of the GaAs bandgap 3 and retaining high quality, atomically sharp ErAs/GaAs interfaces 4,5 . The composite systems display tunable photo-carrier relaxation with ultrashort relaxation times spanning two orders of magnitude 3,6 , while achieving greater film quality 1,7-9 and transport characteristics than low temperature grown GaAs 1,10-16 . These features have made the ErAs:GaAs system highly promising for integration into GaAs-based opto-electronic devices 6,14,[17][18][19][20][21] .…”

“…These studies utilize the bonding differences between the ErAs rocksalt and GaAs zinc blende crystal structures, which introduce localized trap states into the bandgap of GaAs 13,22 . The trap states act as non-radiative recombination sites for photo-excited GaAs carriers 3,6,23,24 , and carrier trapping times are altered by varying superlattice spacing 3,23 .…”

“…Time-resolved conductivity measurements of ErAs:GaAs superlattice composites have indicated GaAs photo-carriers are captured by the interface states within a few ps of excitation 23 . Further, the trapping times vary with ErAs-incorporated layer spacing, suggesting that decreasing the distance between ErAs nanoparticles decreases the amount of time excited carriers travel before being captured by the interface states 3,6,23,24 . As the excitation energy is not sufficient to excite carriers across the GaAs bandgap, the initial response at zero time delay is the result of carriers excited from the interface states into the GaAs conduction band being captured by the traps.…”