Steven R. Bentley

Continuous flow in open microfluidics using controlled evaporation

This paper presents a method for programming the flow rate of liquids inside open microfluidic networks (MFNs). A MFN comprises a number of independent flow paths, each of which starts with an open filling port, has a sealed microchannel in which assays can be performed, and an open capillary pump (CP). The MFN is placed over Peltier elements and its flow paths initially fill owing to capillary forces when liquids are added to the filling ports. A cooling Peltier element underneath the filling ports dynamically prevents evaporation in all filling ports using the ambient temperature and relative humidity as inputs. Another Peltier element underneath the CPs heats the pumps thereby inducing evaporation in the CPs and setting the flow rate in the microchannels. This method achieves flow rates in the microchannels ranging from approximately 1.2 nL s(-1) to approximately 30 pL s(-1), and is able to keep 90% of a 0.6 microL solution placed in an open filling port for 60 min. This simple and efficient method should be applicable to numerous assays or chemical reactions that require small and precise flow of liquids and reagents inside microfluidics.

Growth of strained InGaSb quantum wells for p-FET on Si: Defects, interfaces, and electrical properties

A study of heteroepitaxial molecular beam epitaxy growth of strained p-channel InGaSb quantum well (QW) on lattice mismatched Si (100) using Al(Ga)Sb metamorphic buffers is presented in this paper. The migration enhanced epitaxy (MEE) technique was employed for AlSb nucleation layer (NL) on Si and analyzed using atomic force microscopy and in-situ Auger electron spectroscopy techniques to optimize growth conditions for continuous 2D buffer layers and improve surface quality of subsequent layers. Growth-related defects (threading dislocations, microtwins, and antiphase boundaries) and their effect on surface morphology and electrical properties of the QWs are analyzed with scanning electron microscope and transmission electron microscopy and correlated to the NL properties. The baseline data for defect density in the layers and resultant surface morphology are presented. Room temperature p-channel Hall mobility of 660 cm2/V s at 3 × 1011 cm−2 sheet hole concentration is achieved in InGaSb QWs using an opti...

MBE growth and digital etch of GaSb/InAs nanowires on Si for logic applications

The 6.1 A III–V “high-mobility” semiconductor family includes materials with beneficial transport properties of both electrons and holes (InAs, GaSb), which are appealing for fast and low-power complementary metal–oxide–semiconductor applications. Yet their large lattice mismatch with Si (∼12%) results in three dimensional island nucleation and therefore growth defects. The solution for deposition of this high mismatch material is the growth of the entire device from a single nucleus, such as in vertical nanowires. Two types of GaSb nanowires (NWs) are demonstrated on a Si(111) substrate: vertically stacked InAs/GaSb NWs and coaxial core/shell NWs. This paper summarizes surface preparation, growth conditions, and postprocessing steps which can be used to create nanowires with small enough diameters for use as logic devices.The 6.1 A III–V “high-mobility” semiconductor family includes materials with beneficial transport properties of both electrons and holes (InAs, GaSb), which are appealing for fast and low-power complementary metal–oxide–semiconductor applications. Yet their large lattice mismatch with Si (∼12%) results in three dimensional island nucleation and therefore growth defects. The solution for deposition of this high mismatch material is the growth of the entire device from a single nucleus, such as in vertical nanowires. Two types of GaSb nanowires (NWs) are demonstrated on a Si(111) substrate: vertically stacked InAs/GaSb NWs and coaxial core/shell NWs. This paper summarizes surface preparation, growth conditions, and postprocessing steps which can be used to create nanowires with small enough diameters for use as logic devices.

Electrical properties related to growth defects in metamorphic GaSb films on Si

This paper reports on correlation of growth-related defects and electrical properties in GaSb films grown on different Si substrates using metamorphic buffers. Large lattice mismatch between GaSb and Si (∼11%) results in the formation of threading dislocations (TDs) and microtwins (MTs) along with antiphase domains due to the lack of inversion symmetry in III-Vs. The defect density profiles were analyzed using transmission electron microscopy and atomic force microscopy. The TD density of just below 108 cm−2 and MT density below 104 cm−1 were found in 2.1 μm thick structures, and were found to be four times higher than in similar GaSb structures on GaAs substrates. Hole density and mobility profiles were obtained using differential Hall method and show that dislocations (TDs or MT partials) generate about 25 acceptors/nm. Minimum midgap interface trap density values are similar in the metal-oxide-semiconductor structures prepared on GaAs and Si, ∼2 × 1012 cm2 eV−1.