Impurity-free Vacancy Disordering Research Articles

Influence of SiO2 and TiO2 dielectric layers on the atomic intermixing of InxGa1−xAs/InP quantum well structures

We have studied the influence of SiO2 and TiO2 dielectric layers on the atomic intermixing of InxGa1−xAs/InP quantum well structures using the impurity-free vacancy disordering technique. Photoluminescence results revealed that an enhancement of interdiffusion was obtained when the samples were capped with SiO2. Although TiO2 layers were able to suppress the interdiffusion in the InGaAs/InP system, the suppression was not significant compared to the AlGaAs/GaAs system. Based on a fitting procedure that was deconvoluted from the photoluminescence spectra as well as a theoretical modeling, the electron–heavy hole and electron–light hole transitions were identified, and a ratio of the group V to the group III diffusion coefficients (k) was obtained. The k ratio of the InGaAs/InP samples capped with SiO2 is relatively larger than that of samples capped with TiO2 layers.

25-W 915-nm Lasers With Window Structure Fabricated by Impurity-Free Vacancy Disordering (IFVD)

We have demonstrated high-performance broad-area single-emitter lasers with window structure fabricated by newly developed impurity-free vacancy disordering (IFVD) technique. A very high pulse output power of 25 W was obtained in 100-m wide lasers without facet degradation.

Band gap gratings using quantum well intermixing for quasi-phase-matching

In this work, the spatial resolution of two quantum well intermixing processes has been obtained using spatially resolved photoluminescence. The processes investigated are impurity-free vacancy disordering using SiO2∕SiO2:P caps and sputtered silica induced intermixing. These studies aimed to choose a suitable intermixing technology to realize the band gap gratings for domain disordering quasi-phase-matching in GaAs∕AlGaAs heterostructures. From the photoluminescence studies it was established that the process of impurity-free vacancy disordering using SiO2∕SiO2:P caps has a spatial resolution on the order of 7μm, while the process of sputtered silica induced intermixing has a spatial resolution on the order of 3μm. From these measurements it was demonstrated that the sputtered silica induced intermixing process is more suitable for the fabrication of the gratings needed for quasi-phase-matching in the samples studied here. Successful quasi-phase-matching demonstrated through second harmonic generation at 775nm has been produced in GaAs∕AlAs short superlattice waveguides using sputtered silica induced intermixing through domain disordering quasi-phase-matching. The gratings have shown a duty cycle far from the targeted 1:1 design, which has implications on the conversion efficiency.

Impurity free vacancy disordering of InAs/GaAs quantum dot and InAs/InGaAs dot-in-a-well structures

Two types of InAs quantum dot (QD) structure, grown by molecular-beam epitaxy on GaAs (100) substrates, one with dot-in-a-In 0.12Ga 0.88As quantum well (QW) and another one with dots embedded in a GaAs matrix, were intermixed by impurity free vacancy disordering method using SiO 2 dielectric capping and rapid thermal annealing (RTA). The material and optical qualities of these structures were examined and compared by transmission electron microscopy (TEM) and low-temperature 5 K photoluminescence (PL) measurements. For both structures, significant blueshift of the PL spectra with increasing RTA temperature is observed. A maximum blueshift of up to 325 nm is observed from the InAs/InGaAs structure at a RTA temperature of 900 °C. Deduced from the reduction in dot height/diameter aspect ratio by TEM study and the reduction in PL peak separation for ground and excited states, it appears that QDs in dot-in-a-GaAs structure dissolved in a faster rate with increasing RTA temperature, attributed to the higher strain-induced interdiffusion in the InAs/GaAs structure. As opposed to InAs/GaAs QDs, InAs/InGaAs dots-in-a-well retained their optical quality and structural sharpness even after transforming into a QW at high annealing temperature, thus making this structure better candidate for monolithic photonic integration.

Band gap blue shift of InGaAs/InP multiple quantum wells by different dielectric film coating and annealing

Band gap blue shift of InGaAs/InP multiple quantum well (MQW) structures by impurity-free vacancy disordering (IFVD) is studied by photoluminescence (PL) and secondary ion mass spectrum (SIMS). SiO 2, Si 3N 4, and spin on glass (SOG) were used for the dielectric layers to create the vacancies. The results indicate that the band gap blue shift varies with the different dielectric layers and depends on the annealing temperature. The blue shift is also related to the combination of the layers between dielectric and cladding layers. The SIMS profile shows that the dielectric capped layer and rapid thermal annealing caused the quantum well intermixing, which results in the band gap blue shift. Optimum condition can be reached by choosing suitable dielectric layer and annealing condition.

Luminescent characteristics of InGaAsP/InP multiple quantum well structures by impurity-free vacancy disordering

InGaAsP/InP multiple quantum wells with quantum well intermixing (QWI) have been prepared by Impurity-Free Vacancy Disordering (IFVD). The luminescent characteristics were investigated using photoluminescence (PL) and photoreflectance (PR), from which the band gap blueshift was observed. Si 3N 4, SiO 2 and SOG (spin on glass) were used for the dielectric layer to enhance intermixing from the out-diffusion of Group III atoms. All samples were annealed by rapid thermal annealing (RTA). The results indicate that the band gap blueshift varies with the dielectric layers and the annealing temperature. The SiO 2 capping was successfully used with an InGaAs cladding layer to cause larger band tuning effect in the InGaAs/InP MQWs than the Si 3N 4 capping with an InGaAs cladding layer. On the other hand, samples with the Si 3N 4–InP cap layer combination also show larger energy shifts than that with SiO 2–InP cap layer combination.

Fabrication of multi-wavelength In0.2Ga0.8As/GaAs multiple quantum well laser diodes by area-selective impurity-free vacancy disordering using SiOx capping layers with different stoichiometries

This work studied the implementation of multi-wavelength laser diodes on a single substrate through the position-dependent bandgap modification of the In0.2Ga0.8As/ GaAs multiple quantum wells (MQWs) by impurity-free vacancy disordering (IFVD). The position-dependent bandgap modification is achieved by performing the IFVD with SiOx capping layers with different stoichiometries. The lasing wavelength difference of about 31 nm was obtained between the ridge-waveguide laser diodes fabricated with the MQWs that had undergone the same thermal treatments using the SiOx film provided with SiH4 flow rates of 20 and 300 sccm. The device performance was not appreciably degraded in the laser diodes fabricated with the MQWs that had undergone the IFVD process .

Group-V intermixing in InAs∕InP quantum dots

Postgrowth intermixing in InAs∕InP quantum dot (QD) structures have been investigated by rapid thermal annealing and laser irradiation techniques. In both cases, room-temperature photoluminescence (PL) measured from the QD structures after intermixing shows a substantial blueshift accompanied by an improvement in PL intensity and a reduction in linewidth. In the case of impurity free vacancy disordering, an energy shift of up to 350meV has been achieved. The maximum differential energy shift for samples capped with SiO2 and SiNx dielectrics was found to be 90meV. On the other hand, laser-induced intermixing allows differential energy shifts of more than 250meV in this material system. Micro-Raman measurement shows the appearance of InAs-type and InP-type optical phonon peaks from laser-annealed InAs∕InP QDs due to the exchange of As and P at the QD interfaces.

Study of intermixing in InGaAs∕(Al)GaAs quantum well and quantum dot structures for optoelectronic∕photonic integration

Two of the most important intermixing techniques, ion implantation and impurity free vacancy disordering, are investigated and compared in InGaAs/(Al)GaAs quantum well (QW) and quantum dot (QD) structures. For ion implantation induced intermixing, arsenic implantation was performed and the amount of interdiffusion created was found to vary as a function of implantation dose and temperature. Impurity free vacancy disordering was also enhanced by deposition of SiO 2 in both QW and QD structures and annealing at different temperatures. In order to obtain large differential energy shifts for device integration using both methods, the essential issue of suppression of thermal interdiffusion using a TiO 2 capping layer was also addressed.

Impurity free vacancy disordering of InGaAs quantum dots

The effect of thermal interdiffusion on In(Ga)As∕GaAs quantum dot structures is very significant, due to the large strain and high concentration of indium within the dots. The traditional high temperature annealing conditions used in impurity free vacancy disordering of quantum wells cannot be used for quantum dots, as the dots can be destroyed at these temperatures. However, additional shifts due to capping layers can be achieved at low annealing temperatures. Spin-on-glass, plasma enhanced chemical vapor deposited SiO2, Si3N4, and electron-beam evaporated TiO2 layers are used to both enhance and suppress the interdiffusion in single and stacked quantum dot structures. After annealing at only 750°C the different cappings enable a shift in band gap energy of 100meV to be obtained across the sample.

Influence of semiconductor cap layer on the impurity-free vacancy disordering of the In0.2Ga0.8As/GaAs multiquantum-well structure by dielectric capping layers

The feasibility of normal GaAs, low-temperature-grown GaAs (LT-GaAs) and low-temperature-grown InGaAs (LT-InGaAs) as the capping layers for impurity-free vacancy disordering (IFVD) of the In0.2Ga0.8As/GaAs multiquantum-well (MQW) structure has been studied. The normal GaAs, LT-GaAs and LT-InGaAs layers were tested as the outermost capping layer and the intermediate cap layer underneath the SiO2 or Si3N4 capping layer. The degree of quantum-well intermixing (QWI) induced by rapid thermal annealing was estimated by the shift of the photoluminescence (PL) peak energy. It was found that the IFVD of the In0.2Ga0.8As/GaAs MQW structure using LT-GaAs (LT-InGaAs) as the outermost capping layer was much smaller (larger) than that using a SiO2 (Si3N4) capping layer. It was also observed that the insertion of the normal GaAs, LT-GaAs and LT-InGaAs cap layers below the SiO2 or Si3N4 capping layer reduces the degree of QWI and the PL intensity after the QWI. A plausible explanation for the influence of normal GaAs, LT-GaAs and LT-InGaAs cap layers for the QWI of the InGaAs/GaAs structure is also discussed.

Impurity free vacancy disordering of self‐assembled InGaAs quantum dots by using PECVD‐grown SiO 2 and SiN x capping films

Impurity free vacancy disordering (IFVD) of InGaAs self-assembled quantum dots (SAQDs) grown by metal organic chemical vapor deposition (MOCVD) method has been carried out at 700�°C for the time range from 1 min to 4 min by using SiO2 and SiNx–SiO2 dielectric capping layers. The photoluminescence (PL) peak was blue shifted up to 157 meV and its full width at half maximum (FWHM) was narrowed from 76 meV to 47 meV as the annealing time increased. The integrated PL intensity was increased after the thermal annealing, which may be attributed to a defect quenching. There was an optimum annealing condition to get the largest integrated PL intensity for each dielectric capping. SiNx–SiO2 double capping layers have been found to induce larger integrated PL intensity and better carrier confinement after the thermal annealing of SAQDs compared to SiO2 single capping layer, even though SiNx–SiO2 double capping induced larger blue-shift than SiO2 single capping.

Suppression of interdiffusion in InGaAs/GaAs quantum dots using dielectric layer of titanium dioxide

In this work, titanium dioxide (TiO2) film was deposited onto the In0.5Ga0.5As/GaAs quantum-dot structure by electron-beam evaporation to investigate its effect on interdiffusion. A large redshifted and broadened spectrum from the dot emission was observed compared with that from the uncapped (but annealed) reference sample, indicating the suppression of thermal interdiffusion due to TiO2 deposition. The structure was also capped with a silicon dioxide (SiO2) single layer or SiO2/TiO2 bilayer with the thickness of SiO2 varied from ∼6 to ∼145 nm. In the former case, an increased amount of impurity-free vacancy disordering (IFVD) was introduced with the increase of SiO2 thickness due to the enhanced Ga outdiffusion into the film. With TiO2 deposited on top, IFVD and thermal interdiffusion were suppressed to different extents with the variation of SiO2 thickness. To explain the suppression of interdiffusion, thermal stress introduced by the large thermal expansion coefficient of TiO2 (when compared with GaAs) as well as the metallurgical reactions between the TiO2 and GaAs were proposed as possible mechanisms.

Fabrication of wavelength-shifted In0.2Ga0.8As/GaAs multiple quantum well laser diodes by impurity-free vacancy disordering at different thermal annealing temperatures

We fabricated ridge-waveguide laser diodes with In0.2Ga0.8As/GaAs multiple quantum wells (MQWs) that have undergone impurity-free vacancy disordering (IFVD) using the SiO2 capping layer. The SiO2-capped MQW samples were annealed by rapid thermal annealing (RTA) at different temperatures. The magnitude of the blueshift estimated by the shift of photoluminescence peak energy increases with the increase of RTA temperature due to the enhanced interdiffusion of the MQWs. The electrical characteristics and lasing performance of the annealed laser diodes were compared with those of the as-grown laser diode. The operation wavelengths of 967, 946 and 927 nm with device performance comparable to that of the as-grown device were obtained in the laser diodes fabricated by the MQWs that have undergone IFVD at 850, 900 and 950 °C for 50 s, respectively. Thus, the RTA for the IFVD employed to fabricate wavelength-shifted laser diodes is believed not to seriously degrade the electrical and optical properties of the devices.

Suppression of interdiffusion in GaAs/AlGaAs quantum-well structure capped with dielectric films by deposition of gallium oxide

In this work, different dielectric caps were deposited on the GaAs/AlGaAs quantum well (QW) structures followed by rapid thermal annealing to generate different degrees of interdiffusion. Deposition of a layer of GaxOy on top of these dielectric caps resulted in significant suppression of interdiffusion. In these samples, it was found that although the deposition of GaxOy and subsequent annealing caused additional injection of Ga into the SiO2 layer, Ga atoms were still able to outdiffuse from the GaAs QW structure during annealing, to generate excess Ga vacancies. The suppression of interdiffusion with the presence of Ga vacancies was explained by the thermal stress effect which suppressed Ga vacancy diffusion during annealing. It suggests that GaxOy may therefore be used as a mask material in conjunction with other dielectric capping layers in order to control and selectively achieve impurity-free vacancy disordering.

Influence of dielectric deposition parameters on the In0.2Ga0.8As/GaAs quantum well intermixing by impurity-free vacancy disordering

We investigated the influence of the deposition parameters of SiOx and SiNx capping layers in the plasma-enhanced chemical vapor deposition on the band gap energy shift of the In0.2Ga0.8As/GaAs multiple quantum well (QW) structures induced by impurity-free vacancy disordering. The investigated deposition parameters were deposition pressure, deposition temperature, and rf power. A blueshift of photoluminescence (PL) peak energy up to 161 meV was observed after rapid thermal annealing at 950 °C for 50 s in the samples capped with SiOx deposited at 1.5 Torr. We observed that the blueshift of the PL peak energy increased greatly with the increase of deposition pressure and slightly with the decrease of deposition temperature. The influence of rf power was found to be negligible. All these dependences were related to the porosity in the dielectric capping layers in the QW intermixing.

Dependence of band gap energy shift of In0.2Ga0.8As/GaAs multiple quantum well structures by impurity-free vacancy disordering on stoichiometry of SiOx and SiNx capping layers

We have investigated the effects of the stoichiometry of SiOx and SiNx capping layers on the band gap energy shift induced by impurity-free vacancy disordering of the In0.2Ga0.8As/GaAs multiple quantum well structures. The stoichiometry of the SiOx and SiNx capping layers was changed by varying the flow rate of silane (SiH4) gas, and argon gas was employed as the carrier gas of the diluted SiH4 gas to eliminate any possible incorporation of nitrogen into the deposited film when nitrogen gas is employed as the carrier gas. A blueshift of photoluminescence peak of up to 112 meV is observed after rapid thermal annealing at 950 °C for 50 s from the sample capped with SiOx (provided with a SiH4 flow rate of 20 sccm). It is observed that the magnitude of the blueshift increases with the decrease of SiH4 flow rate for the SiOx and SiNx capping layer because of the increased porosity of dielectric capping layers. The insertion of intermediate GaAs cap layer reduces the band gap energy shift irrespective of the SiOx or SiNx capping layer.

Spectral Response Modification Of Quantum Well Infrared Photodetector By Quantum Well Intermixing

ABSTRACTWe have studied the change of the spectral response in a quantum well infrared photodetector (QWIP) by using the impurity-free vacancy disordering (IFVD) to change the bandgap of the GaAs/AlGaAs multiple quantum well absorption layer. IFVD process has been carried out with PECVD-grown SiO2 capping on the MOCVD-grown QWIP structure, whose absorption region consists of 25 periods of 3.6nm thick Si-doped GaAs well and 50nm thick Al0.24Ga0.76As barrier. The PL peak of MQW decreased with the increase of annealing temperature and time from 802 nm to 700 nm at 15 K. The fabricated QWIP whose absorption region was intermixed at 850 °C by IFVD technique showed the maximum change in spectral response from 8 to 10 um when compared to a QWIP without intermixing. This result implies that the intermixing technology can be used to make multicolor QWIP without growing multiple IR absorption regions.

Luminescent Characteristics of InGaAsP/InP Multiple Quantum Well Structures by Impurity-Free Vacancy Disordering

AbstractInGaAsP/InP multiple quantum wells have been prepared by Impurity-Free Vacancy Disordering (IFVD). The luminescent characteristics was investigated using photoluminescence (PL) and photoreflectance (PR), from which the band gap blue shift was observed. Si3N4, SiO2 and SOG were used for the dielectric layer to create the vacancies. All samples were annealed by rapid thermal anne aling (RTA). The results indicate that the band gap blue shift varies with the dielectric layers and annealing temperature. The SiO2 capping was successfully used with an InGaAs cladding layer to cause larger band tuning effect in the InGaAs/InP MQWs than the Si3N4 capping with an InGaAs cladding layer. On the other hand, samples with the Si3N4-InP cap layer combination also show larger energy shifts than that with SiO2-InP cap layer combination.

Luminescent Characteristics of InGaAsP/InP Multiple Quantum Well Structures by Impurity-Free Vacancy Disordering

AbstractInGaAsP/InP multiple quantum wells have been prepared by Impurity-Free Vacancy Disordering (IFVD). The luminescent characteristics was investigated using photoluminescence (PL) and photoreflectance (PR), from which the band gap blue shift was observed. Si3N4, SiO2 and SOG were used for the dielectric layer to create the vacancies. All samples were annealed by rapid thermal anne aling (RTA). The results indicate that the band gap blue shift varies with the dielectric layers and annealing temperature. The SiO2 capping was successfully used with an InGaAs cladding layer to cause larger band tuning effect in the InGaAs/InP MQWs than the Si3N4 capping with an InGaAs cladding layer. On the other hand, samples with the Si3N4-InP cap layer combination also show larger energy shifts than that with SiO2-InP cap layer combination.