Mechanism of polarization pinning in vertical cavity surface emitting lasers using focused ion beam etching

Photoluminescence experiments have identified strain as the origin for polarization pinning in vertical cavity surface emitting lasers post-processed by focused ion beam etching. Theoretical models were applied to deduce the strain in devices. Post-annealing was used to optimize polarization pinning.

High power laser with integrated lens using focused ion beam etching

In this study, a collimating lens is introduced at the output facet of a tapered waveguide laser to compensate for the divergence of the optical mode. The collimating lens is shown to enhance the laser efficiency while simultaneously reducing the far field divergence.

Focused ion beam etching of GaN

We have investigated the use of focused ion beam (FIB) etching for the fabrication of GaN-based devices. Although work has shown that conventional reactive ion etching (RIE) is in most cases appropriate for the GaN device fabrication, the direct write facility of FIB etching - a well-established technique for optical mask repair and for IC failure analysis and repair - without the requirement for depositing an etch mask is invaluable. A gallium ion beam of about 20nm diameter was used to sputter GaN material. The etching rate depends linearly on the ion dose per area with a slope of 3.5×10 -4μm3/pC. At a current of 3nA, for example, this corresponds to an etch rate of 1.05μm3/s. Good etching qualities have been achieved with a side wall roughness significantly below 0.1μm. Changes in the roughness of the etched surface plane stay below 8nm.

Thickness control of Molecular Beam Epitaxy grown layers at the 0.01-0.1 monolayer level

Electron tunnelling through semiconductor tunnel barriers is exponentially sensitive to the thickness of the barrier layer, and in the most common system, the AlAs tunnel barrier in GaAs, a one monolayer variation in thickness results in a 300% variation in the tunnelling current for a fixed bias voltage. We use this degree of sensitivity to demonstrate that the level of control at 0.06 monolayer can be achieved in the growth by molecular beam epitaxy, and the geometrical variation of layer thickness across a wafer at the 0.01 monolayer level can be detected.

Occurrence of particle debris field during focused Ga ion beam milling of glassy carbon

To explore the machining characteristics of glassy carbon by focused ion beam (FIB), particles induced by FIB milling on glassy carbon have been studied in the current work. Nano-sized particles in the range of tens of nanometers up to 400 nm can often be found around the area subject to FIB milling. Two ion beam scanning modes - slow single scan and fast repetitive scan - have been tested. Fewer particles are found in single patterns milled in fast repetitive scan mode. For a group of test patterns milled in a sequence, it was found that a greater number of particles were deposited around sites machined early in the sequence. In situ EDX analysis of the particles showed that they were composed of C and Ga. The formation of particles is related to the debris generated at the surrounding areas, the low melting point of gallium used as FIB ion source and the high contact angle of gallium on glassy carbon induces de-wetting of Ga and the subsequent formation of Ga particles. Ultrasonic cleaning can remove over 98% of visible particles. The surface roughness (Ra) of FIB milled areas after cleaning is less than 2 nm. © 2010.

Ion beam, focused ion beam, and plasma discharge machining

Non-conventional methods of machining are used for many engineering applications where the traditional processes fail to be cost-effective. Such processes include Ion Beam Machining (IBM), focused ion beam (FIB) machining and plasma discharge machining. The mechanisms of material removal and associated hardware and software developed for industrial applications of these fascinating electro-physical and chemical machining processes are reviewed together with the latest research findings. © 2009 CIRP.

Influence of AlN Buffer Thickness on GaN Grown on Si(111) by Gas Source Molecular Beam Epitaxy with Ammonia

Hexagonal GaN is grown on a Si(111) substrate with AlN as a buffer layer by gas source molecular beam epitaxy (GSMBE) with ammonia. The thickness of AlN buffer is changed from 9 to 72 nm. When the thickness of AlN buffer is 36 nm, the surface morphology and crystal quality of GaN is optimal. The in-situ reflection high energy electron diffraction (RHEED) reveals that the transition to a two-dimensional growth mode of AlN is the key to the quality of GaN. However, the thickness of AlN buffer is not so critical to the residual in-plane tensile stress in GaN grown on Si(111) by GSMBE for AlN thickness between 9 to 72 nm.

Influence of V/III ratio on the structural and photoluminescence properties of In0.52AlAs/In0.53GaAs metamorphic high electron mobility transistor grown by molecular beam epitaxy

A series of metamorphic high electron mobility transistors (MMHEMTs) with different V/III flux ratios are grown on GaAs (001) substrates by molecular beam epitaxy (XIBE). The samples are analysed by using atomic force microscopy (AFM), Hall measurement, and low temperature photoluminescence (PL). The optimum V/III ratio in a range from 15 to 60 for the growth of MMHEMTs is found to be around 40. At this ratio, the root mean square (RMS) roughness of the material is only 2.02 nm; a room-temperature mobility and a sheet electron density are obtained to be 10610.0cm(2)/(V.s) and 3.26 x 10(12)cm(-2) respectively. These results are equivalent to those obtained for the same structure grown on InP substrate. There are two peaks in the PL spectrum of the structure, corresponding to two sub-energy levels of the In0.53Ga0.47 As quantum well. It is found that the photoluminescence intensities of the two peaks vary with the V/III ratio, for which the reasons are discussed.

Optimization of metamorphic InGaAs quantum wells on GaAs grown by molecular beam epitaxy

We investigate the molecular beam epitaxy growth of metamorphic InxGa(1-x)As materials (x up to 0.5) on GaAs substrates systematically. Optimization of structure design and growth parameters is aimed at obtaining smooth surface and high optical quality. The optimized structures have an average surface roughness of 0.9-1.8 nm. It is also proven by PL measurements that the optical properties of high indium content (55%) InGaAs quantum wells are improved apparently by defect reduction technique and by introducing Sb as a surfactant. These provide us new ways for growing device quality metamorphic structures on GaAs substrates with long-wavelength emissions.

Evolution of surface morphology and photoluminescence characteristics of 1.3-mu m In0.5Ga0.5As/GaAs quantum dots grown by molecular beam epitaxy

Evolution of surface morphology and optical characteristics of 1.3-mu m In0.5Ga0.5As/GaAs quantum dots (QDs) grown by molecular beam epitaxy (MBE) are investigated by atomic force microscopy (AFM) and photoluminescence (PL). After deposition of 16 monolayers (ML) of In0.5Ga0.5As, QDs are formed and elongated along the [110] direction when using sub-ML depositions, while large size InGaAs QDs with better uniformity are formed when using ML or super-ML depositions. It is also found that the larger size QDs show enhanced PL efficiency without optical nonlinearity, which is in contrast to the elongated QDs.