V. P. Evtikhiev

Time-resolved photoluminescence measurements of InAs self-assembled quantum dots grown on misorientated substrates

Time-resolved photoluminescence decay measurements have been performed on samples with varying-sized self-assembled InAs/GaAs quantum dot ensembles, formed by substrate misorientation. Ground-state radiative recombination lifetimes from 0.8 to 5.3 ns in the incident power density range of 0.05–3400u2002Wu200acm−2 at a temperature of 77 K have been obtained. It was found that a reduction of the quantum dot size led to a corresponding reduction of the radiative lifetime. The evident biexponential decay was obtained for the ground state emission of the quantum dot array, with the slower second component attributed to a carrier recapturing process.

Voltage distributions and nonoptical catastrophic mirror degradation in high power InGaAs/AlGaAs/GaAs lasers studied by Kelvin probe force microscopy

Kelvin probe force microscopy is used to observe the bulk potential redistribution across the high power InGaAs/AlGaAs/GaAs separate confinement heterostructure quantum-well laser diodes for a wide range of injection currents, including the lasing regime. By increasing the injection current, the development of a parasitic voltage drop is detected at initial calibration layers and the buffer layer of the laser structure. Catastrophic degradation of the laser mirror was observed at the level of injection current ∼19 times the threshold value. Atomic force microscopy images of the mirror revealed a 100 nm deep crater of maximum width ∼2.5 μm in the vicinity of the buffer/emitter interface. By combining the surface morphology results of the destructed mirror with those of Kelvin probe force microscopy in operating devices, it is concluded that the parasitic voltage drop is responsible for a substantial energy dissipation and the nonoptical degradation of the laser mirror.

Characteristics of the InAs quantum dots MBE grown on the vicinal GaAs(0 0 1) surfaces misoriented to the [0 1 0] direction

Abstract Atomic-force microscopy is used to study InAs quantum dot arrays grown by molecular beam epitaxy on vicinal GaAs(0xa00xa01) surfaces misoriented to the [0xa01xa00] direction by 1°, 2°, 4°, and 6°. For a chosen misorientatoin direction, it is shown that the vicinal GaAs(0xa00xa01) surface is covered with a net of stepped terraces. The condensation of the network of terraces upon increasing of the misorientation angle leads to the suppression of adatom surface diffusion and makes it possible to achieve higher densities and better uniformity of quantum dots arrays.

Kelvin probe force and surface photovoltage microscopy observation of minority holes leaked from active region of working InGaAs∕AlGaAs∕GaAs laser diode

A method for direct observation of carrier leakage from active regions of working semiconductor light-emitting diodes and lasers is suggested. In this method, Kelvin probe force and surface photovoltage microscopies are used to measure local changes in the surface potential of the device mirror on which a high concentration of the leaked carriers is expected. The applicability of the method is demonstrated by studying in detail the leakage current on the mirrors of high-power InGaAs∕AlGaAs∕GaAs laser diodes in action. It is shown that minority holes arrive at the mirror surface from the active zone of the laser and spread over to regions of the n emitter and n substrate. This observation is confirmed by exposing the mirror to external light with photon energy exceeding the band gap of the laser structure and measuring the generated surface photovoltage. Owing to surface channels formed by the surface band bending, the holes can move tens of micrometers from the place of their generation. The leakage curre...

Effect of GaAs (001) Surface Misorientation on the Emission from MBE Grown InAs Quantum Dots

The photoluminescence (PL) is used to study the capped InAs quantum dot (QD) single sheet array MBE grown on the vicinal GaAs(0 0 1) surfaces misoriented to the [0 1 0] direction by 0°, 2°, 4°, 6°. The misorientation leads to the blue shift and the narrowing of InAs QD PL lines and makes PL efficiency higher. These effects are related, respectively, with the smaller size and higher size uniformity of the InAs QDs and reduction of the number of large InAs islands on the misoriented surfaces. It was found that the decrease of the growth interruption time between the end of QDs growth and the start of the GaAs layer overgrowth makes these modifications of the PL spectra with surface misorientation stronger and the efficiency of the PL higher. With the use of misoriented substrates, single sheet QD laser with threshold current density of 210 A/cm 2 at room temperature was realized.

Observation of the biexponential ground-state decay time behavior in InAs self-assembled quantum dots grown on misoriented substrates

Biexponential behavior of the time-resolved photoluminescence decay from the ground state has been studied over a temperature range of 77–300 K on samples with varying sized self-assembled InAs∕GaAs quantum dot ensembles controlled by substrate misorientation alone. The slower second decay component is considerably longer than the first one, and has been measured to be as long as 300 ns. This slow component is attributed to carrier recapturing and indirect radiative recombination processes.

Spectroscopic studies of random telegraph noise in InAs quantum dots in GaAs

We have observed and investigated random telegraph noise in the photoluminescence from InAs quantum dots in GaAs. The luminescence from a single quantum dot, exhibiting switching between two levels, has been spectrally resolved. The random telegraph noise is only observed in the presence of band filling. We find no spectral shift of the emission in the different states. It is only the intensity, mainly for higher energy peaks, that changes. The InAs quantum dots behave similarly to InP/GaInP and InGaAs/GaAs quantum dots, with respect to random telegraph noise.

Study of high-power GaAs-based laser diodes operation and failure by cross-sectional electrostatic force microscopy

One of the important factors that restricts the power limit of semiconductor lasers is a catastrophic optical mirror damage. This process is significantly suppressed through decreasing the optical power density due to its redistribution over the broad transverse waveguide (BW). Recently it was shown that record-breaking values of the quasicontinuous and continuous-wave (QWC and CW) output power for 100-μm-wide-aperture devices can be achieved by incorporating a broad transverse waveguide into 0.97 μm emitting Al-free InGaAs(P)/InGaP/GaAs and Al-containing InGaAs/AlGaAs/GaAs separate confinement heterostructure quantum-well lasers (SCH-QWL). Another important factor limiting the CW output power is the Joule overheating of a laser diode due to an extra serial resistance. Traditionally, a decrease in the resistance is achieved by development of the contacts, whereas a voltage distribution across the device structure is not analyzed properly. At high operating currents the applied voltage can drop not only across the n-p-junction, but also at certain additional regions of the laser structure depending on a particular design of the device. Electrostatic force microscopy (EFM) provides a very promising method to study the voltage distribution across an operating device with a nanometer space resolution. An application of EFM for diagnostics of III-V laser diodes without and under applied biases have been recently demonstrated. However, the most interesting range of the biases, the lazing regime, has not been studied yet.

Photoluminescence decay time measurements from self-organized InAs/GaAs quantum dots grown on misoriented substrates

Time-resolved photoluminescence (PL) was studied to determine the radiative recombination lifetimes in InAs/GaAs quantum dots (QDs) fabricated on misoriented substrates by the Stransky-Krastanov method. The intensity of PL from the ground state, excited state and wetting layer of QD was also studied as a function of the excitation density. Measured lifetimes were as high as 3.1?ns. The measurements have clearly demonstrated the band state filling effect: it also provides the possibility of estimating the excitation power density corresponding to the manifestation of this effect at the excitation power of 30?A?cm-2.

Giant enhancement of terahertz emission from nanoporous GaP

In this paper, we have studied the emission of terahertz radiation from nanoporous semiconductor matrices of GaP excited by the femtosecond laser pulses. We observe 3–4 orders of magnitude increase of terahertz radiation emission from the nanoporous matrix compared to bulk material. The effect is mainly related to drastic increase of the sample surface and pinning of conducting electrons to surface states. This result opens up a promising way to create powerful sources of terahertz radiation using nanoporous semiconductors.