Neng Liu

Enhanced photoluminescence emission from bandgap shifted InGaAs/InGaAsP/InP microstructures processed with UV laser quantum well intermixing

In spite of many years of research, the quantum well intermixing technique has not been able to deliver multibandgap III–V semiconductor wafers at highly attractive costs. We report that UV laser irradiation of InGaAs/InGaAsP/InP quantum well (QW) microstructures in deionized water and rapid thermal annealing (RTA) allows achieving, mask-free, wafers with blueshifted photoluminescence (PL) emission of intensity exceeding almost 10× that of the RTA-only wafers. Our calculations indicate that a ∼40 nm thick InOx layer formed on top of the investigated microstructure induces compressive strain in the QW region and leads to this record-high enhanced PL amplitude. (Some figures may appear in colour only in the online journal) The selective area control of the bandgap of semiconductor wafers is one of the key factors in the development of photonic integrated circuits (PICs) (Estrella et al 2012). Post-growth quantum well intermixing (QWI) has been reported as a relatively simple and potentially cost-effective method allowing area-selective bandgap tuning of Si/Si1−xGex (Dubowski et al 1999) and III–V quantum well (QW) wafers (Skogen et al 2005, Genest et al 2008, Xu and Mei 2009,

Carrier-induced fast wavelength switching in tunable V-cavity laser with quantum well intermixed tuning section.

We report on the fast wavelength switching in V-cavity laser (VCL) with quantum well intermixed tuning section. The laser wavelength can be switched between 32 channels at 100 GHz spacing using a single electrode control. The fabrication process involves a quantum well intermixing (QWI) process using KrF laser irradiation and rapid thermal annealing (RTA). The tuning current is less than 40 mA, much lower than previously demonstrated tunable VCL based on electro-thermal-optic effect. The wavelength switching is also faster by three orders of magnitude. The dynamic switching characteristics between two channels with different numbers of intermediate channels are investigated. It shows that the switching time is about 1 ns between adjacent channels and increases up to 12 ns with increasing number of intermediate channels.

Selective area in situ conversion of Si (001) hydrophobic to hydrophilic surface by excimer laser irradiation in hydrogen peroxide

We report on a method of rapid conversion of a hydrophobic to hydrophilic state of an Si (0 0 1) surface irradiated with a relatively low number of pulses of an excimer laser. Hydrophilic Si (0 0 1), characterized by the surface contact angle (CA) of near 15 ◦ ,i s fabricated following irradiation with either KrF or ArF excimer lasers of hydrophobic samples (CA ∼ 75 ◦ ) immersed in a 0.01% H2O2/H2O solution. The chemical and structural analysis carried with x-ray photoelectron spectroscopy and atomic force microscopy measurements confirmed the formation of OH-terminated Si (0 0 1) surface with no detectable change in the surface morphology of the laser-irradiated material. To investigate the efficiency of this laser-induced hydrophilization process, we demonstrate a selective area immobilization of biotin-conjugated fluorescein-stained nanospheres outside of the laser-irradiated area. The results demonstrate the potential of the method for the fabrication of biosensing architectures and advancements of the Si-based microfluidic device technology.

Surface morphology of SiO2 coated InP/InGaAs/InGaAsP microstructures following irradiation with the ArF and KrF excimer lasers

Successful fabrication of devices from quantum well-intermixed material requires efficient control of its surface morphology. To address this problem, we have employed atomic force microscopy to study surface morphology of InP/InGaAs/InGaAsP QW microstructure coated with dSiO2 = 50, 150, 190, 243 and 263 nm thick SiO2 films. Both ArF (193 nm) and KrF (248 nm) excimer lasers have been used to irradiate series of samples with up to 400 pulses of fluence 76 to 156 mJ/cm2. The roughness (σRMS) of SiO2 layer after both lasers irradiation and RTA decreases as the pulse number increases. Following RTA, a smoother surface morphology was observed for all irradiated samples. The cap InP layer was found to have a relatively smaller roughness (~ 0.4 nm) due to the protection provided by the SiO2 layer during excimer laser irradiation and high temperature RTA. For samples coated with 50- or 150-nm-thick SiO2 and irradiated by the ArF laser, the blueshift is only obtained when the SiO2 layer was ablated. However, the sample coated with 243-nmthick SiO2 (dSiO2 ≈ λKrF), following the 75-pulse-irradiation with the KrF laser at 124mJ/cm2 and RTA, showed a smooth surface (σRMS = 1.8 nm) and maximum blueshift of 74 nm achieved without removal of the SiO2 layer.

Photocorrosion metrology of photoluminescence emitting GaAs/AlGaAs heterostructures

High sensitivity of the photoluminescence (PL) effect to surface states and chemical reactions on surfaces of PL emitting semiconductors has been attractive in monitoring photo-induced microstructuring of such materials. To address the etching at nano-scale removal rates, we have investigated mechanisms of photocorrosion of GaAs/Al0.35Ga0.65As heterostructures immersed either in deionized water or aqueous solution of NH4OH and excited with abovebandgap radiation. The difference in photocorrosion rates of GaAs and Al0.35Ga0.65As appeared weakly dependent on the bandgap energy of these materials, and the intensity of an integrated PL signal from GaAs quantum wells or a buried GaAs epitaxial layer was found dominated by the surface states and chemical reactivity of heterostructure surfaces revealed during the photocorrosion process. Under optimized photocorrosion conditions, the method allowed resolving a 1 nm thick GaAs sandwiched between Al0.35Ga0.65As layers. We demonstrate that this approach can be used as an inexpensive, and simple room temperature tool for post-growth diagnostics of interface locations in PL emitting quantum wells and other nano-heterostructures.

XPS study of InP/InGaAs/InGaAsP microstructures irradiated with ArF laser in air and deionized water

Excimer lasers, due to their compatibility with a large-scale industrial production, are attractive tools for precise processing of photonic and microelectronic materials. In this article, we discuss the effect of ArF excimer laser defect formation on the surface of InP/InGaAs/InGaAsP quantum well (QW) microstructures irradiated in air and deionized (DI) water environments. Structural defects on surfaces of such QW materials have been known to induce vacancy diffusion towards the QW region and lead to the so called quantum well intermixing (QWI) effect during the rapid thermal annealing step. Excimer lasers have been used to create surface defects on InP/InGaAs/InGaAsP microstructure and induce QWI during high temperature annealing. Chemical composition of the QW microstructures irradiated with ArF laser in air and DI water is studied with X-ray photoelectron spectroscopy to investigate both the formation and role of the surface defects in the laser-induced QWI process.

ArF excimer laser-induced quantum well intermixing in dielectric layer coated InGaAs/InGaAsP microstructures

It has been known that excimer laser irradiation of surfaces of III-V quantum well (QW) semiconductor microstructures can be used for selective area bandgap engineering of such materials [1]. Depending on the laser used, investigated microstructure and the irradiation environment both enhanced quantum well intermixing (QWI) leading to blue shifting of the bandgap energy [2], as well as suppressed QWI [3] processes have been reported. Excimer lasers are attractive for bandgap engineering as they can be used to pattern large size wafers, often in a single step, and without the need of using photolithography masks that normally are required to achieve selective area processing.To investigate the role of the solid environment and the influence of laser-induced surface defects on the amplitude of the QWI process, we have investigated InP/InGaAs/InGaAsP QW microstructure coated with 2 sets of SiO2 layers having distinctively different optical properties. An ArF (193 nm) laser has been used to irradiate a series of samples with up to 400 pulses of fluence 76 mJ/cm2. The bandgap shift of irradiated sites, following two 120 sec rapid thermal annealing steps at 650°C and 675°C, varies with the pulse fluence and number. A maximum of 120 nm blueshift of the bandgap was observed for the samples irradiated with 150 pulses of the laser. We have also investigated the ArF laser QWI on the QW microstructure coated with layers of Si3N4. We discuss the advantages of this approach for post growth fabrication of multibandgap QW material suitable for designing and manufacturing of monolithically integrated photonic devices.It has been known that excimer laser irradiation of surfaces of III-V quantum well (QW) semiconductor microstructures can be used for selective area bandgap engineering of such materials [1]. Depending on the laser used, investigated microstructure and the irradiation environment both enhanced quantum well intermixing (QWI) leading to blue shifting of the bandgap energy [2], as well as suppressed QWI [3] processes have been reported. Excimer lasers are attractive for bandgap engineering as they can be used to pattern large size wafers, often in a single step, and without the need of using photolithography masks that normally are required to achieve selective area processing.To investigate the role of the solid environment and the influence of laser-induced surface defects on the amplitude of the QWI process, we have investigated InP/InGaAs/InGaAsP QW microstructure coated with 2 sets of SiO2 layers having distinctively different optical properties. An ArF (193 nm) laser has been used to irradiate a series...

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75°. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm(2), respectively, has decreased the CA to near 15°, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafers surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm(2) and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103°. The XPS results indicate ArF laser induced formation of Si-(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals.

Multi section bandgap tuned superluminescent diodes fabricated by UV laser induced quantum well intermixing

Superluminescent diodes are used in numerous sensing and testing applications. To achieve the wide emission spectrum and high power required from such devices, we studied an innovative design constituting in several different bandgap energy sections independently electrically pumped. Bandgap modification was obtained by the UV laser quantum well intermixing process.