Impurity-free Vacancy Disordering Research Articles

Research on the fabrication of high-power semiconductor lasers by impurity-free vacancy disordering

Research on the fabrication of high-power semiconductor lasers by impurity-free vacancy disordering

Wide-gap photoluminescence control of quantum dots through atomic interdiffusion and bandgap renormalization

Abstract Bandgap and photoluminescence (PL) energy control of epitaxially grown II–VI quantum dots (QDs) are highly desirable for applications in optoelectronic devices, yet little work has been reported. Here, we present a wide tunability of PL emission for CdTe/ZnTe QDs through an impurity-free vacancy disordering method. To induce compressive stress at the dielectric layer/ZnTe interface, a SiO2 film is deposited onto the samples, followed by rapid thermal annealing to induce atomic interdiffusion. After the heat treatment, the PL spectra of the intermixed QDs show pronounced blueshifts in peak energy as large as ∼200 meV because of the reduced bandgap renormalization and decreased quantum confinement effects in addition to the dominant atomic interdiffusion effect. In addition, we present a thorough investigation on the modified physical properties of the intermixed QDs, including their lattice structure, thermal escape energy, and carrier dynamics, through quantitative X-ray and optical characterizations.

Study on the proximity of QWI in InP-based AlGaInAs MQWs using the IFVD method and its application in single frequency teardrop laser diodes.

This paper presents our research on quantum well intermixing (QWI) of InP-based AlGaInAs/AlGaInAs multi-quantum wells using impurity-free vacancy-disordering (IFVD) and the QWI mask proximity effect and its application in the design and fabrication of a teardrop laser. Using a Si3N4 film deposited by plasma-enhanced chemical vapor deposition (PECVD) as a QWI promoter mask and annealing under 700°C for 2 minutes, a 70 nm wavelength blue shift of a FP laser is achieved using InP-based AlGaInAs quantum well laser material. It is found that a 5 µm separation is needed between the QWI mask edges and the non-QWI area during the QWI process. Based on the QWI technique and proximity effect, the designed and fabricated teardrop laser demonstrated continuous wave (CW) lasing above 40 mA and single frequency operation with a side mode suppression ratio of 32.6 dB at 77.3 mA.

Conservation of quantum efficiency in quantum well intermixing by stress engineering with dielectric bilayers

In semiconductor lasers, quantum well intermixing (QWI) with high selectivity using dielectrics often results in lower quantum efficiency. In this paper, we report on an investigation regarding the effect of thermally induced dielectric stress on the quantum efficiency of quantum well structures in impurity-free vacancy disordering (IFVD) process using photoluminescence and device characterization in conjunction with microscopy. SiO2 and SixO2/SrF2 (versus SrF2) films were employed for the enhancement and suppression of QWI, respectively. Large intermixing selectivity of 75 nm (125 meV), consistent with the theoretical modeling results, with negligible effect on the suppression region characteristics, was obtained. SixO2 layer compensates for the large thermal expansion coefficient mismatch of SrF2 with the semiconductor and mitigates the detrimental effects of SrF2 without sacrificing its QWI benefits. The bilayer dielectric approach dramatically improved the dielectric–semiconductor interface quality. Fabricated high power semiconductor lasers demonstrated high quantum efficiency in the lasing region using the bilayer dielectric film during the intermixing process. Our results reveal that stress engineering in IFVD is essential and the thermal stress can be controlled by engineering the dielectric strain opening new perspectives for QWI of photonic devices.

Monolithic Fabrication of InGaAs/GaAs/AlGaAs Multiple Wavelength Quantum Well Laser Diodes via Impurity-Free Vacancy Disordering Quantum Well Intermixing

InGaAs/GaAs/AlGaAs multiple wavelength quantum well (QW) semiconductor laser diodes (LDs) have been fabricated by impurity-free vacancy disordering (IFVD) QW intermixing (QWI) method. The IFVD-QWI process was carried out by sputtering-depositing SiO2 mask layers on top of the complete InGaAs/GaAs/AlGaAs QW laser structure, emitting at 980 nm wavelength, and followed by a rapid thermal annealing at 880 °C for 60 s. The lasing wavelength of the devices fabricated from the intermixed wafer was blue-shifted with the increase of the mask layer thickness. The maximum emission wavelength blue shift of a processed as-cleaved laser reached 112 nm with the output-power more than 1000 mW. By using such an IFVD-QWI technique, multi-wavelength integrated LDs have also been successfully fabricated from a single chip.

Impurity Free Vacancy Disordering (IFVD) of InGaAs/AlGaAs Quantum Well Laser Structures

Impurity free vacancy disordering (IFVD) has been used to investigate the atomic interdiffusion of InGaAs/InGaAs quantum well laser structures using double-crystal X-ray diffraction (DCXRD) and photoluminescence measurements. X-ray measurements showed that some part of the carbon was electrically activated after annealing without a dielectric capping layer, but not after annealing with a TiO2 capping layer. For a SiO2 capping layer, the tensile peak was still observed after annealing which is comparable to the samples annealed without capping layer. Photoluminescence results showed that a large energy shift was observed when the samples were coated with SiO2. A negligible photoluminescence shift was observed after annealing when the samples coated with TiO2.

Sub‐1100 nm lasing from post‐growth intermixed InAs/GaAs quantum‐dot lasers

Impurity free vacancy disordering induced highly intermixed InAs/GaAs quantum-dot lasers are reported with high internal quantum efficiency (>89%). The lasers are shown to retain the device characteristics after intermixing and emitting in the important wavelength of ∼1070–1190 nm. The non-coated facet Fabry-Pērot post-growth wavelength tuned lasers exhibits high-power (>1.4W) and high-gain (∼50 cm−1), suitable for applications in frequency doubled green–yellow–orange laser realisation, gas sensing, metrology etc.

无杂质空位诱导量子阱混杂研究及应用现状

无杂质空位诱导量子阱混杂研究及应用现状

Enhanced Impurity-Free Intermixing Bandgap Engineering for InP-Based Photonic Integrated Circuits

Impurity-free intermixing of InGaAsP multiple quantum wells (MQW) using sputtering Cu/SiO2 layers followed by rapid thermal processing (RTP) is demonstrated. The bandgap energy could be modulated by varying the sputtering power and time of Cu, RTP temperature and time to satisfy the demands for lasers, modulators, photodetector, and passive waveguides for the photonic integrated circuits with a simple procedure. The blueshift of the bandgap wavelength of MQW is experimentally investigated on different sputtering and annealing conditions. It is obvious that the introduction of the Cu layer could increase the blueshift more greatly than the common impurity free vacancy disordering technique. A maximum bandgap blueshift of 172 nm is realized with an annealing condition of 750°C and 200s. The improved technique is promising for the fabrication of the active/passive optoelectronic components on a single wafer with simple process and low cost.

InGaAs/GaAsP/GaInP quantum well lasers with window structure fabricated by impurity free vacancy disordering

In order to fabricate 940nm InGaAs/GaAsP/GaInP semiconductor lasers with non-absorbing window (NAW), the induced quantum well intermixing (QWI) is investigated using impurity free vacancy disordering (IFVD) method. Successful intermixing is obtained with 24nm bandgap blue shift between the window and gain regions. Under destructive testing conditions, the catastrophic optical damage (COD) power for the NAM LD is about 116% higher than the conventional LD.

High-Efficient and Reliable Broad-Area Laser Diodes With a Window Structure

We report on high-power 915-nm broad-area laser diodes with a window structure formed by a impurity-free vacancy disordering method. A maximum conversion efficiency of 68% and high output power of 19.8 W have been achieved at 20°C. A stable operation over 2000 h has also been confirmed under the condition of an output power of 15 W at 25°C. Far-field patterns suggest that the laser diode is suitable for coupling into an optical fiber with 105-μm core diameter and 0.15 numerical aperture.

Intermixing of InGaAs/GaAs quantum wells and quantum dots using sputter-deposited silicon oxynitride capping layers

Various approaches can be used to selectively control the amount of intermixing in III-V quantum well and quantum dot structures. Impurity-free vacancy disordering is one technique that is favored for its simplicity, however this mechanism is sensitive to many experimental parameters. In this study, a series of silicon oxynitride capping layers have been used in the intermixing of InGaAs/GaAs quantum well and quantum dot structures. These thin films were deposited by sputter deposition in order to minimize the incorporation of hydrogen, which has been reported to influence impurity-free vacancy disordering. The degree of intermixing was probed by photoluminescence spectroscopy and this is discussed with respect to the properties of the SiOxNy films. This work was also designed to monitor any additional intermixing that might be attributed to the sputtering process. In addition, the high-temperature stress is known to affect the group-III vacancy concentration, which is central to the intermixing process. This stress was directly measured and the experimental values are compared with an elastic-deformation model.

Built-in electric field influence on impurity-free vacancy disordering of InGaAs/InP quantum well structure

Built-in electric field may enhance or retard the impurity-free vacancy disordering (IFVD) during rapid thermal annealing (RTP) by imposing a drift on charged point defects. Built-in electric field is at the interface between dielectric layer and top layer of the structure. Subsequent rapid thermal annealing leads to different intermixing results due to different field directions on InP cap layers in different doping types. Experimental results also show different influences of the built-in field on the two sublattices largely due to different charge numbers of point defects.

Investigations of impurity-free vacancy disordering in (Al)InGaAs(P)/InGaAs quantum wells

In this work, controlled band gap modifications in InGaAsP/InGaAs and AlInGaAs/InGaAs quantum well structures using different encapsulating layers are studied and compared. Photoluminescence spectroscopy was used for monitoring the changes in the optical properties of the quantum wells due to interdiffusion. X-ray photoelectron spectroscopy was used to investigate the interfacial reaction between the QW structure and dielectric capping layer. The results are compared and discussed based on the sublattices' interdiffusion, promotion or suppression under different dielectric capping layers.

Cap Layer Influence on Impurity-Free Vacancy Disordering of InGaAs/InP Quantum Well Structure

Quantum well intermixing (QWI) by the impurity-free vacancy disordering (IFVD) technique is an important and effective approach for the monolithic integration of optoelectronic devices based on InGaAs/InP quantum well structures. We experimentally investigate the influence of the capping layer SiO2 and Si3N4 on the QWI by IFVD. The results show that for all the samples with three-types differently doped (P, N and I) top InP layers, Si3N4 can always induce a larger photoluminescence blueshift than SiO2 in the IFVD QWI process, which attributes more to the group III and V vacancies point defects created in the interface of Si3N4-InP than that of SiO2-InP, proved by the SIMS measurements. The inherent mechanisms for explaining these properties are further discussed.

DIRECT IMPRINTING OF SiO2 WAVEGUIDE STRUCTURES ON GaAs AND ITS APPLICATION IN InAs/GaAs QUANTUM DOT INTERMIXING

A novel approach for intermixing of InAs / GaAs quantum dot (QD) structure by direct imprinting of SiO 2 strips using silicafilm is presented. The silicafilm SiO 2 strips were imprinted on a InAs / GaAs QD structure by an Obducat nanoimprinter using a polyethylene terepthalate soft mold. Inductively coupled plasma etching of GaAs waveguide structures using the imprinted SiO 2 strips as hard mask has been demonstrated. By using the silicafilm SiO 2 as a capping layer, the effects of impurity-free vacancy disordering intermixing on optical characteristics of the InAs / GaAs QD structure have been examined. The measured photoluminescence spectra of the InAs / GaAs QD structure suggest that differential wavelength blueshift of up to 105 nm for region with and without the SiO 2 film can be achieved. A cost effective one step SiO 2 hard mask with graded thickness profile for quantum well or QD intermixing by imprinting technique is proposed for application in broadband lasers and superluminescent diodes.

Selective disordering of InAs/InGaAs dots-in-a-well structure patterned with sol-gel derived SiO2 strips imprinted by soft mold technique

Selective impurity free vacancy disordering of InAs/InGaAs quantum dot (QD) structures imprinted with sol-gel derived SiO2 strips via a polyethylene terepthalate soft mold has been investigated. Wavelength blueshift of up to 220 nm for areas capped with the sol-gel derived SiO2 is demonstrated. The imprinted SiO2 strips were used as hard mask for plasma etching of GaAs ridge waveguide structures and were found to have similar hardness as the SiO2 prepared by plasma-enhanced chemical vapor deposition. QD intermixing using sol-gel derived SiO2 with step-thickness profile was demonstrated, and a one-step SiO2 imprinting technique for multiple band gap QD intermixing is proposed.

Intermixing of InP-based multiple quantum wells for integrated optoelectronic devices

The intermixing characteristics of three widely used combinations of InP-based quantum wells (QW) are investigated using the impurity-free vacancy disordering (IFVD) technique. We demonstrate that the bandgap energy shift is highly dependent on the concentration gradient of the as-grown wells and barriers, as well as the thickness of the well, with thinner wells more susceptible to interdiffusion at the interface between the barrier and well. According to our results, the InGaAsP/InGaAsP and InGaAs/InP are well suited for applications requiring a wide range of bandgap values within the same wafer. In the case of the InGaAs/InGaAsP system, its use is limited due to the significant broadening of the photoluminescence spectrum that was observed. The effect of the top InGaAs layer over the InP cladding is also investigated, which leads to a simple way to obtain three different bandgaps in a single intermixing step.

High Power and High Reliable 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. Vacancies induce quantum well intermixing, leading to bandgap shift. We have succeeded in obtaining the large bandgap shift in window region and maintaining the original bandgap in gain region simultaneously. We can control the bandgap difference. A very high output power of 25.6W at 30A under pulsed operation was obtained without facet degradation. This is the one of the highest power for 100μm wide single emitter lasers. Moreover, no degradation and no sudden failure were observed for 5800 hours life test at 8W-20°C. We have, thus, realized the highest output power and high reliable lasers with window structure fabricated by IFVD.

Quantum Dash Intermixing

We investigate the intermixing effect in InAs/InAlGaAs quantum-dash-in-well structures grown on InP substrate. Both impurity-free vacancy disordering (IFVD) via dielectric cap annealing, and impurity-induced disordering (IID) using nitrogen ion-implantation techniques have been employed to spatially control the group-III intermixing in the quantum-dash (Qdash) system. Differential bandgap shifts of up to 80 nm and 112 nm have been observed from the IFVD and IID processes, respectively. Compared to the control (nonintermixed) lasers, the light-current characteristics for the 125 nm wavelength shifted Qdash lasers are not significantly changed, suggesting that the quality of the intermixed material is well preserved. The intermixed lasers exhibit a narrower linewidth as compared to the as-grown laser due to the improved dash homogeneity. The integrity of the material is retained after intermixing, suggesting the potential application for the planar integration of multiple active/passive Qdash-based devices on a single InP chip.