Properties of Defect Traps in Triple-Stack InAs/GaAs Quantum Dots and Effect of Annealing

Journal of Applied Physics

Wang

2007

The electron-emission properties of relaxation-induced traps in InAs/GaAs quantum dots ͑QDs͒ are studied in detail using capacitance-voltage ͑C-V͒ profiling and bias-dependent deep-level transient spectroscopy. Strain relaxation is shown to induce a threading-dislocation-related trap in the top GaAs layer and a misfit-dislocation-related trap near the QD. The threading trap decreases its electron-emission energy from 0.63 to 0.36 eV from sample surface toward the QD, whereas the misfit trap gradually increases its electron-emission energy from 0.28 to 0.42 eV from near the QD toward the GaAs bottom layer, indicating that both traps near the QD have lower electron-emission energies. Hence, the emission-energy change is attributed to the related traps across the QD interface where a band offset exists. The C-V profiling at 300 K shows extended carrier depletion near the QD. As temperature is increased, an electron-emission peak emerges at the QD followed by a prominent peak, suggesting that the trap responsible for the prominent peak lies in energy below the QD electron ground state. From a simulation, this trap is identified to be the misfit trap located at the QD and at the observed emission energy below the GaAs conduction band. Based on the energy location of this trap, we deduce a possible mode of strain relaxation.

Section: Methodsmentioning

confidence: 91%

Electron emission properties of relaxation-induced traps in InAs/GaAs quantum dots and the effect of electronic band structure

Journal of Applied Physics

Wang

2007

“…Detail growth conditions can be found elsewhere. 13 A QD sheet density about 3 ϫ 10 10 cm −2 was observed by atomic field microscopy ͑AFM͒ images. For capacitance-voltage ͑C − V͒ profiling, Schottky diodes were realized by evaporating Al on the sample.…”

mentioning

confidence: 94%

Strain relaxation in InAs∕InGaAs quantum dots investigated by photoluminescence and capacitance-voltage profiling

Hsiao

Applied Physics Letters

et al. 2005

We present detailed studies of the onset of strain relaxation in InAs/ InGaAs quantum dots. We show that the ground-state photoluminescence ͑PL͒ emission redshifts with increasing the InAs coverage before relaxation and blueshifts when relaxation occurs. PL spectra of the relaxed samples show two predominant families of dots with very different temperature-dependent efficiency. By comparison we show that the dots emitting at long wavelength are degraded by relaxation while the dots emitting at short wavelength remain coherently strained. Consequently, the PL spectra are dominated by the dots emitting at short wavelength, leading to the observed blueshift. This result suggests that the relaxation does not occur uniformly. In addition, we show that the relaxation occurs in the dot bottom interface.

“…Detailed growth conditions can be found elsewhere. 24 A typical QD sheet density of about 3 ϫ 10 10 cm −2 was observed by atomic force microscopy ͑AFM͒. Postgrowth annealing was performed by rapid thermal annealing.…”

Section: Methodsmentioning

confidence: 99%

Influence of thermal annealing on the electron emission of InAs quantum dots containing a misfit defect state

Journal of Applied Physics

Yang

Hsu

et al. 2009

We have investigated the effect of postgrowth thermal annealing on the electron emission from InAs quantum dots ͑QDs͒ containing a misfit-related defect state induced by strain relaxation. Additional carrier depletion in the GaAs bottom layer near the QD, caused by the defect state, can effectively suppress electron tunneling from the QD, leading to the observation of a thermal emission from the QD electron ground state to the GaAs conduction band with a large emission energy of 213 meV, in contrast to defect-free nonrelaxed QDs in which an emission of 58 meV from the QD electron ground state to first excited state is observed. The emission energy is reduced to 193 meV and to 164 meV after annealing at 650 and 700°C for 1 min, respectively. This emission energy reduction is correlated with the photoluminescence blueshift which is attributed to the interdiffusion of atoms across the QD interface. The electron emission from the QD first excited and ground states is found to be a thermal emission at high temperatures and a tunneling emission at low temperatures. The tunneling energy barrier is found to be comparable to the thermal emission energy, supporting a thermal emission to the GaAs conduction band. This study illustrates a significant effect of a defect state on the electron-emission process in the QDs, suggesting the possibility of modifying the electron emission time of the QDs by purposely introducing a deep defect state.