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The room-temperature active modulation of plasmonic nanolasers is demonstrated on the hybrid graphene–insulator–metal (GIM) platform. The threshold and lasing intensity of ZnO plasmonic nanolasers are modulated by injecting the current into the graphene layer in order to break the Lorentz reciprocity in the plasmonic cavity. The laser threshold increases with the external current injection, and a 0.17-nm Doppler shift is observed with 120-mA external current injection. The theoretical model is constructed that takes both the nonreciprocal effect and thermal effect induced by the current injection into consideration. The nanolaser operated at room temperature and with the functionality of threshold modulation on the GIM platform shall be very promising in the development of integrated photonic circuits.

We demonstrate that local oxidation of silicon nitride films deposited on conductive substrates with a conductive-probe atomic force microscope (AFM) is a very promising approach for nanofabrication. Scanning Auger microscopy and spectroscopy are employed to verify the chemical changes after AFM-induced oxidation. Furthermore, the growth kinetics are found to have a logarithmic relationship of oxide height versus pulse duration [h∝ln(t/t0)]. In contrast to rather slow thermal oxidation process, AFM-induced oxidation on silicon nitride has an anomalously high initial oxidation rate (∼30 000 nm/s at 10 V) and a small onset time t0 (∼10 μs). As for the applications in ultrahigh-density recording, an oxide dot array (∼100 Gbit/in.2) produced by this process is demonstrated. The nitride film patterned by AFM can be utilized as an etching mask to fabricate “subtractive” silicon nanostructures, due to the large etching selectivity of Si3N4:SiO2:Si in various etchants. With this method, which is entirely compatible with the existing microelectronic processes, synthesis of ultrahigh packing density and ordered nanostructures could become readily achievable.

We report the investigation of coherent GaN nanocrystals spontaneously formed by nitrogen-plasma-assisted reactive epitaxy with Ga droplets supported on the single crystalline Si3N4(0001)∕Si(111) surface. The distribution of grown GaN nanocrystals, as revealed by scanning electron microscopy and cross-sectional transmission electron microscopy, is very uniform in size (∼16nm) and shape and the distribution width is significantly narrower than that of Ga droplets deposited in the Volmer–Weber mode. By using high-resolution electron microscopy, the shape and crystalline structure of the self-assembled GaN nanocrystals can be determined to be truncated triangular pyramids formed by the facets of the GaN wurtzite lattice.

High-quality InN epitaxial films have been grown by nitrogen-plasma-assisted molecular-beam epitaxy on Si(111) substrates using a double-buffer technique. Growth of a (0001)-oriented single crystalline wurtzite–InN layer was confirmed by reflection high-energy electron diffraction, x-ray diffraction, and Raman scattering. At room temperature, these films exhibited strong near-infrared (0.6–0.9 eV) photoluminescence (PL). In addition to the optical absorption measurement of absorption edge and direct band nature, the PL signal was found to depend linearly on the excitation laser intensity over a wide intensity range. These results indicate that the observed PL is due to the emission of direct band-to-band recombination rather than the band-to-defect (or impurity) deep emission.

We present a stacked buffer mechanism for heteroepitaxial growth with large lattice mismatch. The stacked buffer consists of constituent layers, which can form coincident lattices at layer/layer and layer/substrate interfaces. For the case of GaN-on-Si(111) heteroepitaxy, we utilize the 1:2 and 5:2 coincident lattices formed at the β-Si3N4(0001)/Si(111) and AlN(0001)/β-Si3N4(0001) interfaces, respectively, to facilitate the double-buffer layer for GaN-on-Si heteroepitaxial growth. By using this buffer technique, we resolve the issue of autodoping resulting from Si outdiffusion when grown with a single AlN(0001) buffer. As a result, the epitaxial quality of GaN film is also significantly improved.

We report on the development of a new two‐dimensional micropositioning device, or walker, which is capable of moving across very large distances (in principle unlimited) and with a very small step size (as small as 100 A/step) in both directions. Based on a unique tracking design, the motion is extremely orthogonal with very little crosstalk between the two directions. Additionally, there is no detectable backlash in either direction. The walker performance has been extensively tested by using a position‐sensitive proximitor probe. Tests have been done between 77 and 300 K. However, we project that the walker will be able to operate at temperatures as low as 4 K. This walker system has shown extremely reliable performance in a UHV environment for use with scanning tunneling microscopy and has been especially useful for cross‐sectional scanning tunneling microscopy and spectroscopy studies of semiconductor hetero‐ and homostructures. We show one example of results on the (AlGa)As/GaAs heterostructure system.

Due to their high aspect ratio, well-defined cylindrical structure, and good electrical conductivity, carbon nanotubes (CNTs) are ideal probes for “true” local imaging of electric domain structures at the nanoscale. By performing force–distance measurements and tip-shape profiling with a uniformly charged oxide square, we clearly demonstrate the local nature of the CNT tip for electrostatic force microscopy. We show that CNTs can be used to probe long-range electrostatic forces with a lateral resolution better than 5 nm.

The biased conductive probe of an atomic force microscope can induce local oxidation in ambience for converting silicon nitride films to silicon oxides with high reaction rate. Spatially resolved photoemission analysis with submicron resolution has been utilized to study the oxidation states of converted silicon oxide patterns in comparison with the surrounding Si3N4 layer. The core level shift of the Si 2p photoelectron peak and the spectral features in the valence band reveal a complete conversion of silicon nitride to silicon oxide at a bias voltage of 10 V, with no remaining nitrogen left. The major oxide is SiO2. The observed oxidation states of Si4+, Si3+, and Si2+ show a gradient depth distribution indicating excess silicon in the layer.

We report selective epitaxial growth of Si using an ultrathin bilayer mask. The key feature of this process is direct writing of nanoscale patterns by means of local anodic oxidation of a Si3N4 layer using an atomic force microscope operated in air. Windows for selective growth are defined by wet etching of the locally oxidized regions. High growth selectivity upon chemical vapor deposition of Si is accomplished by employing the bilayer mask structure which is formed by oxidizing the Si3N4 surface and then selectively desorbing SiO2 in the windows. High-quality homoepitaxial growth is verified by transmission electron microscopy. We also report a simple plasma-treatment technique which solves the problem of retarded SiO2 desorption in the nanoscale windows.

It has been found that atomic force microscope (AFM) induced local oxidation is an effective way for converting thin (

We have demonstrated that silicon nanostructures with high aspect ratios, having ∼400 nm structural height and ∼55 nm lateral dimension, may be fabricated by scanning probe lithography and aqueous KOH orientation-dependent etching on the H-passivated (110) Si wafer. The high spatial resolution of fabricated features is achieved by using the atomic force microscope based nano-oxidation process in ambient. Due to the large (110)/(111) anisotropic ratio of etch rate and the large Si/SiO2 etch selectivity at a relatively low etching temperature and an optimal KOH concentration, high-aspect-ratio gratings with (111)-oriented structural sidewalls as well as hexagonal etch pit structures determined by the terminal etch geometry can be obtained.

Nanometer-scale patterning of TiN films grown on SiO2/Si(001) has been demonstrated using the local electric-field-induced oxidation process with a conductive-probe atomic force microscope. The chemical composition of the modified TiN region was determined by micro-Auger electron spectroscopy and was found to consist of Ti, some trace amount of N, and O, suggesting the formation of titanium oxynitride in the near surface region. The dependence of the oxide height on the sample bias voltage with a fixed scanning speed shows a nonlinear trend in the high electric field regime, indicating that the growth kinetics might be significantly different from previous studies using other film materials.

In situ scanning tunneling microscopy and time-resolved reflection high-energy electron diffraction measurements were performed to study the nitridation process of the As-terminated GaAs(001)-(2×4) surface by using electron cyclotron resonance plasma-assisted molecular-beam epitaxy. We report the real-space atomic structure of the coherently strained (3×3)-ordered GaN monolayer on GaAs(001) after a limited-exposure nitridation process and the atomically smooth morphology of this nitrided surface. The unique (3×3) phase is found consisting of nitrogen dimers and a regular array of missing nitrogen rows in both [110] and [110] directions.

We report a cross‐sectional scanning tunneling microscopy investigation of heavily Si doped [001]‐oriented GaAs grown by molecular‐beam epitaxy. At a very high doping level (6×1019 cm−3), Si‐doping induced precipitates are directly observed in XSTM images of the as‐grown epitaxial layers. Most of the precipitates are found to have a characteristic oval shape with the long axis (∼80 A) along the growth direction. In contrast to the low diffusivity of randomly distributed Si dopants in the moderate doping regime, these precipitates are found to be highly mobile and spontaneously form ‘‘nanowires’’ during crystal growth.

Scanning tunneling microscopy (STM) was used to study the (NH4)2S‐passivated (110) cross‐sectional surfaces of both doped and undoped Al0.3Ga0.7As/GaAs heterostructures on n+‐substrates. The ex situ (NH4)2S treatment of the cross‐sectional surfaces of heterostructures was found to be very stable against oxidation. STM images showed no appreciable deterioration of surface quality in vacuum after more than 40 days. The spectroscopic results on the undoped epilayer showed diodelike behavior, confirming that an undoped large band gap region can be imaged by STM through carrier injection from the conductive regions.

We present ultrafast time-resolved optical spectroscopy on GaN nanorods at room temperature. The studied GaN nanorods, with diameters of ∼50 nm and lengths of ∼400 nm, were grown on the silicon substrate. After femtosecond optical pulses excited carriers in the GaN nanorods, the carriers thermalized within a few picoseconds. Subsequently, the electrons are trapped by the surface states on the order of 20 ps. After the surface electric field was reformed in the GaN nanorods, we found the lifetime of the residue carriers in GaN nanorods is longer than 1.7 ns at room temperature, while the lifetime of carriers in GaN thin film is typically a few hundred picoseconds. Our findings indicate that GaN nanorods have higher electrical quality compared with GaN thin film.

Scanning tunneling microscopy and spectroscopy is used to study GaAs multiple pn junction samples cleaved in ultrahigh vacuum. Direct topographic contrast over the pn junctions can be observed in the constant current imaging mode. The topographic height in the p‐type regions appears much lower (by about 5 A) than that in the n‐type regions. Tunneling spectroscopy measurements show consistency with the assignment of the p‐ and n‐type regions. We discuss a possible mechanism for the observed contrast.

Graphene has been regarded as a prospective transparent electrode for a GaN-based light-emitting diode (LED), but fundamental knowledge about the intrinsic properties of the graphene/GaN contact is lacking. We have studied the optical and electronic properties of graphene exfoliated on an n-type GaN surface. The graphene visibility was simulated based on Fresnel's law and confirmed with an optical microscope and micro-Raman spectra. The interfacial electronic property was studied with a scanning photoelectron microscope. We found that the Schottky barrier height of the graphene/n-GaN is decreased with decreasing graphene number of layers, yielding an improved GaN-based LED performance.

We report the nanoscale optical investigation of a single GaN p-n junction nanorod by cathodoluminescence (CL) in a scanning transmission electron microscope. CL emission characteristic of dopant-related transitions was correlated to doping and structural defect in the nanorod, and used to determine p-n junction position and minority carrier diffusion lengths of 650 nm and 165 nm for electrons and holes, respectively. Temperature-dependent CL study reveals an activation energy of 19 meV for non-radiative recombination in Mg-doped GaN nanorods. These results directly correlate doping, structure, carrier dynamics, and optical properties of GaN nanostructure, and provide insights for device design and fabrication.

This study reports on the anisotropic electron transport properties and a correlation between the electron mobility (μ) and the stacking faults (SFs) in the a-plane InN film. Electron mobilities measured by terahertz time-domain spectroscopy and Hall effect measurement along the in-plane [1¯100] (c⊥) orientation were much higher than those of the in-plane [0001] (c∥) orientation. This result shows a sharp contrast to higher defect density for the c⊥ orientation as measured by x-ray diffraction. The electrons transporting through the planar SFs aligned along the c⊥ direction are expected to experience more scattering by defects, resulting in lower μ for the c∥ orientation.

High quality single-crystalline wurtzite indium nitride (InN) thin film was first demonstrated to have a Young's modulus of 149 ± 5 GPa along a-axis using atomic force microscopy microbending test since the revision of InN energy gap. These released InN cantilever beams were examined to have ignorable in-plane residual stress using micro-Raman spectroscopy, where the E2 (high) mode at 490 cm−1 exists zero shift because of the perfect lattice match (8:9 commensurate) between InN and underneath aluminum nitride buffer. The experimental value of Young's modulus agrees well with a number of theoretical estimations ranging from 146 to 159 GPa.

The coupling of plasmonic resonances with the multiple phonon modes of a plasmonic supracrystal is studied. Ultrafast optical pump-probe spectroscopy with variable wavelength allows the selective detection of the breathing mode, the interparticle vibrations, and the vibration of the whole structure. Thanks to this selectivity, the characterization of the bonding strength between nanoparticles in different directions of the supracrystal is possible. The observation of these vibrations could be useful for the realization of future phonon modulated photonic and plasmonic devices.

Terahertz time-domain spectroscopy (THz-TDS) has been used to investigate electrical properties of Mg-doped indium nitride (InN). Mg-doping in InN was found to significantly increase terahertz transmittance. THz-TDS analysis based on the Drude model shows that this high transmittance from Mg-doped InN is mainly due to the reduction in mobility associated with ionized dopants. The Hall-effect-measured mobility is typically lower than the THz-TDS-measured mobility for the same samples. However, the results of both measurements have the same slope in the linear relation between mobility and density. By introducing a compensation ratio of ∼0.2, an excellent agreement in mobilities of two methods is obtained.

ZnO nanorods have been prepared by electrodeposition under identical conditions on various p-GaN-based thin film structures. The devices exhibited lighting up under both forward and reverse biases, but the turn-on voltage and the emission color were strongly dependent on the p-GaN-based structure used. The origin of different luminescence peaks under forward and reverse bias has been studied by comparing the devices with and without ZnO and by photoluminescence and cathodoluminescence spectroscopy. We found that both yellow-orange emission under reverse bias and violet emission under forward bias, which are commonly attributed to ZnO, actually originate from the p-GaN substrate and/or surface/interface defects. While the absolute brightness of devices without InGaN multiple quantum wells was low, high brightness with luminance exceeding 10 000 cd/m2 and tunable emission (from orange at 2.1 V to blue at 2.7 V, with nearly white emission with Commission internationale de l’eclairage (CIE) coordinates (0.30,...

Valence band alignments of wurtzite III-nitride semiconductorheterojunctions are investigated using cross-sectional scanning photoelectron microscopy and spectroscopy on the nonpolar side-facet of a vertically −c-axis-aligned heterostructurenanorod array. The nonpolar measurement geometry and near fully relaxed lattice structure allow for the determination of “natural” band alignments without the influence of spontaneous and piezoelectricpolarization fields. The valence band offsets of InN/GaN, GaN/AlN, and InN/AlN are measured to be 0.8 ± 0.1, 0.6 ± 0.1, and 1.4 ± 0.1 eV, respectively. These results are in good agreement with previous data for heteroepitaxial films and obey the expected transitivity rule.

We report on precise control of film crystal polarity in fully relaxed, thin InN/AlN heterojunctions grown on sapphire by plasma-assisted molecular beam epitaxy. Using these samples, we have measured asymmetric valence band offset values (0.8 {+-} 0.1 eV for the In/Al- and 1.8 {+-} 0.1 eV for the N-polar case) at polar InN/AlN heterojuncitons by synchrotron soft x-ray photoelectron spectroscopy. We confirm that the discontinuities of spontaneous polarizations at polar InN/AlN heterointerfaces lead to the large core level shift of the Al 2p peak related to the In 4d peak (1.0 eV).

The screening effect of heavy-hole LO–phonon interaction is observed and studied through the pump-probe transmission measurement in Mg-doped InN. Combining the measured transient hole dynamics with the absorption spectra, the optical based observation is able to prevent the influence of the surface n-type layer and the depression layer in Mg-doped InN. With the observed heavy-hole heating time at different photoexcited carrier densities and the measured absorption edge, we show that it is now possible to estimate the background hole density and band gap energy in Mg-doped InN.

Subwavelength electroluminescent sources with spatial, spectral, and polarization controlling capabilities are critical elements for optical imaging and lithography beyond the diffraction limit. Here, we show that the electroluminescence from single, strain-free InGaN nanodisks embedded in self-assembled GaN p - n nanorods can span the entire visible spectrum with a large linear polarization ratio ( ∼ 0.85 ) . Furthermore, this unique nanodisk-in-nanorod geometry enables the realization of the ultrasmall footprint light-emitting diodes(LEDs) to be used as subwavelength light sources. Using these nano-LEDs, we are able to demonstrate near-field, subwavelength photolithography by controlling the exposure time and light intensity from single InGaN nanodisks at chosen wavelengths.

A nonpolar stoichiometric InN(11 (2) over bar0) surface freshly cleaved inside UHV was investigated by scanning tunneling microscopy and spectroscopy. Due to the absence of intrinsic surface states in the band gap, scanning tunneling spectroscopy yields directly the fundamental bulk band gap of 0.7 +/- 0.1 eV. The Fermi energy is pinned 0.3 eV below the conduction band minimum due to cleavage induced defect states. Thus, intrinsic electron accumulation can be excluded for this surface. Electron accumulation is rather an extrinsic effect due to surface contamination or material decomposition, but not an intrinsic material property of InN. (C) 2011 American Institute of Physics. [doi:10.1063/1.3553022]

Recent experiments indicate the universality of electron accumulation and downward surface band bending at as-grown InN surfaces with polar or nonpolar orientations. Here, we demonstrate the possibility to prepare flatband InN ( 000 1 ¯ ) surfaces. We have also measured the surface stoichiometry of InN surfaces by using core-level photoelectron spectroscopy. The flatband InN ( 000 1 ¯ ) surface is stoichiometric and free of In adlayer. It implies that the removal of In adlayer at the InN ( 000 1 ¯ ) surface leads to the absence of downward surface band bending. On the other hand, the stoichiometric InN (0001) surface still exhibits surface band bending due to the noncentrosymmetry in the wurtzite structure.

Conventional InGaN/GaN light-emitting diodes based on planar quantum wellstructures do not allow for efficient long-wavelength operation beyond the blue region due to a strong quantum confined Stark effect in lattice-mismatched polar InGaNquantum wells. Here we overcome the limitation by using self-assembled GaNnanorod arrays as strain-free growth templates for thick InGaN nanodisks. In combination with enhanced carrier localization and high crystalline quality, this approach allows us to realize full-color InGaN nanodisk emitters. By tailoring the numbers, positions, and thicknesses of polychromatic nanodisk ensembles embedded vertically in the GaNnanorod p - n junction, we are able to demonstrate natural white (color temperature ∼ 6000 K ) electroluminescence from InGaN/GaN nanorod arrays.

Indium nitride (InN) surfaces treated with ammonium sulfide [(NH4)2Sx] are investigated using Hall effect measurement, x-ray photoelectron spectroscopy (XPS), and scanning Kelvin probe microscopy (SKPM). Upon the (NH4)2Sx treatment, the sheet carrier density is reduced by (0.8–0.9)×1013 cm−2, leading to an increase in the sheet resistance. By numerically solving the Poisson’s equation, the associated upward shift of the surface band bending is derived to be 0.3 eV. XPS characterization shows, on the (NH4)2Sx treated InN surface, the formation of native oxide is effectively suppressed and a covalently bonded sulfur layer with surface In atoms is formed. This surface In–S dipole layer results in an increase in the electron affinity, thus giving rise to a lower surface bending shift (0.2 eV) observed in XPS. The electron affinity increase of 0.1 eV can be deduced, which is consistent with the result obtained by SKPM. Thus, the (NH4)2Sx treatment has been demonstrated to be an effective method for reducing th...

We report that the electron cooling time in indium nitride can be as fast as sub-100 femtosecond at low electron concentration (

We utilize coherent longitudinal optical phonon as an optical nanoprobe to investigate the plasmonic behavior of wurtzite c-plane InN thin films. The transition from the three-dimensional electron gas in InN bulk toward the two-dimensional electron gas in InN thin film is revealed via measuring the coupling strength of coherent A1(LO) phonon and plasmon coupling mode. The coupling strength diminishes as the film thickness reduces and finally vanishes at 3±1 nm. This phenomenon is ascribed to the detuning of the intersubband plasmon frequency above the A1(LO) frequency, which is originated from the electronic quantum confinement in InN thin films.

We report carrier concentration-dependence of terahertz emission from magnesium doped indium nitride (InN:Mg) films. Near the critical concentration (nc∼1×1018 cm−3), the competition between two emission mechanisms determines the polarity of terahertz emission. InN:Mg with n>nc exhibits enhanced positive polarity terahertz emission compared to the undoped InN, which is due to the reduced screening of the photo-Dember field. For InN:Mg with n

Ultrathin {beta}-Si{sub 3}N{sub 4}(0001) epitaxial films formed by N{sub 2}-plasma nitridation of Si(111) substrates have been studied by photoelectron spectroscopy using synchrotron radiation. The valence band offset at the {beta}-Si{sub 3}N{sub 4}/Si interface was determined by valence-band photoelectron spectra to be 1.8 eV. Furthermore, the Si 2p core-level emissions were analyzed for nitride (Si{sup 4+}) and subnitride (Si{sup 3+} and Si{sup +}) components to characterize the interface stoichiometry. In contrast to the interfaces formed by ammonia thermal nitridation and N{sub 2}-plasma nitridation at room temperature, the interface formed by N{sub 2}-plasma nitridation at high substrate temperature is very close to subnitride free with an abrupt composition transition.

The electrical properties of N-polar undoped InN and nonpolar a-InN:Mg ion sensitive field effect transistors (ISFETs) have been investigated by electrolyte-gate-biased current-voltage (IDS-VGS) measurements. IDS-VGS characteristics reveal that the a-InN:Mg ISFETs have a large (∼52%) current variation ratio at a gate bias of 0.3 V with respect to the unbiased one, which is higher than that from the undoped InN ISFETs (∼18% and

uted by them to the existence of high-density steps and defects at the cleavage surface. In this work, we provide direct evidence for the unpinned nature of cleaved a-plane GaN surfaces. Furthermore, we report on the application of XSPEM/S technique for direct imaging of GaN p-n junction. The sample structure for this study is N-polar p-GaN 1.5 m /n-GaN 1.5 m /AlN 25 nm /Si 3 N 4 /Si111, which was grown by plasma-assisted molecular beam epitaxy PA-MBE on a Si wafer. Details of the growth technique can be found elsewhere. 11 The n- and p-type doping was performed by using high-purity Si and Mg solid cells during the PA-MBE growth process. The Mg concentration as determined by secondary ion mass spectroscopy is 7

Time-resolved second harmonic generation is utilized to investigate the photoexcited carrier and phonon dynamics in wurtzite InN nanorods. The exponential decay response in the pump-induced second-harmonic generation curve reveals the carrier relaxation process via radiative and nonradiative recombination channels. Meanwhile, the generation and detection of the coherent A1(LO) phonon can reveal not only the phonon dynamics but also the crystalline quality in InN nanorods. It is found that the nonradiative structural defects play a dominant role in the transport and optical properties of InN nanorods.

A generic method for immobilization of gold nanoparticle bioconjugates onto aluminum nitride (AlN) surfaces using aminosilane molecules as cross-linkers is demonstrated for surface acoustic wave (SAW) sensor applications. Electrostatic interaction between positively charged surface amine groups and negatively charged DNA-Au nanoparticle conjugates allows the self-assembly of a probe nanoparticle monolayer onto functionalized AlN surfaces under physiological conditions. Both 10 and 20 nm Au nanoparticles bound with thiolated oligonucleotides were employed in the detection scheme. We show that Au nanoparticles can play multiple roles in SAW sensing for probe immobilization, signal amplification, and labeling.

The exceptionally large electron affinity of InN causes the pinning of surface Fermi level well above the conduction band minimum. This unique electronic property leads to the electron accumulation at InN surfaces and a large built-in electric field in the topmost few nanometers of InN surfaces. In this letter, we demonstrate that this surface electric field can be unambiguously determined and monitored in a-plane wurtzite InN surface via time-resolved electric-field-induced second harmonic generation. This finding makes it possible to directly probe and characterize the surface electronic properties of Mg-doped InN with an all-optical technique in ambient environment.

Coherent phonon spectroscopy of an a-plane wurtzite InN epitaxial thin film is demonstrated with time-resolved second-harmonic generation technique. Coherent E1(LO) phonons are launched via a transient electric field screening process in the near surface region of the a-plane wurtzite InN. Because of the macroscopic electric dipole interaction between coherent E1(LO) phonons and photoexcited plasmons, two hybridized vibration modes, phononlike (L−) and plasmonlike (L+) E1(LO) phonon-plasmon coupling modes, are identified. The investigation of these coupling modes allows us to understand the ultrafast carrier and phonon dynamics in a-plane wurtzite InN.

Ultrafast carrier thermalization in n-type indium nitride (InN) with an electron concentration of 3.8×1018 cm−3 was investigated by femtosecond transient transmission measurements at room temperature with different wavelengths. An extremely fast carrier external thermalization time on the order of 400 fs was observed, which is much faster than all previous reports. This observed femtosecond thermalization time is consistent with a prediction based on a Coulomb screening effect. Through wavelength dependent and power dependent studies, even with a 400 fs thermalization time, we did not observe any evidence of the existence of the hot phonon effect, which agrees with a recent report that a longitudinal optical phonon lifetime could be shorter than 300 fs in specific InN samples.

Ultrathin (∼10nm) InN ion selective field effect transistors (ISFETs) have been demonstrated to perform ion sensing in aqueous solutions with a sensitivity of 5μA/decade and a response time smaller than 10s. The positively charged surface states on InN surfaces selectively adsorb anions, building Helmholtz voltages in solutions and modulating the drain-source current of the ISFETs. The ISFET performance is greatly enhanced by depleting carriers in the ultrathin InN channel where the film thickness is close to depth of surface electron accumulation.

A method for studying heterojunction band lineups on the submicrometer scale is demonstrated by using synchrotron-radiation photoelectron microscopy and spectroscopy. In particular, an in situ sample cleavage technique is adopted here to reveal the cross-sectional, nonpolar a-plane face of InN∕GaN heterojunction grown on Si(111) along the polar −c axis with fully relaxed lattice structure, eliminating the polarization effects associated with the interface charge/dipole normal to the cleaved surface. The “intrinsic” valence band offset at the cleaved InN∕GaN heterojunction has been determined to be 0.78eV. Additionally, using known material parameters, the values of InN∕GaN conduction band offset and InN electron affinity are also estimated.

We report a significant enhancement in terahertz emission from the indium nitride (InN) films grown along the a axis (a-plane InN), relative to the InN films grown along the c axis. The primary radiation mechanism of the a-plane InN film is found to be due to the acceleration of photoexcited carriers under the polarization-induced in-plane electric field perpendicular to the a axis, which effectively enhances the geometrical coupling of the radiation out of semiconductor. In addition, azimuthal angle dependence measurement shows that the p-polarized terahertz output consists of a large angularly independent component and a weak component with a distinctive fourfold rotation symmetry.

We demonstrate that indium nitride (InN) can be used as ion selective electrode (ISE) for anion concentration measurements. The InN ISE reveals remarkable selectivity, response time, signal stability, and repeatability for chlorine and hydroxyl ions. The selective interaction of Lewis bases in solutions with the N-polarity InN epitaxial layer grown on silicon is confirmed by potentiometric responses. The Helmholtz potential of the InN ISE, generated at the InN/solution interface, satisfies the Nernst equation. The observation of anion attraction to the InN surface further demonstrates the existence of donor-type surface states on InN.

We investigate the position-selected electronic structure of laser modified carbon nanotubes (CNTs) by scanning photoelectron microscopy. After laser pruning removed the top layer of CNTs in air and N2 environment, the modified region shows enhanced chemical shifts of 0.9 and 0.6eV in carbon 1s state, respectively. The modification of electronic structure is shown to be strongly dependent on the gaseous environment. We demonstrate an effective postgrowth process to modify the electronic structure of CNTs for further applications.

Terahertz time-domain spectroscopy has been used to investigate terahertz conductivity and dielectric response of indium nitride (InN) nanorod array and epitaxial film. The complex terahertz conductivity of InN film is well fitted by the Drude model, while the negative imaginary conductivity of the InN nanorods can be described by using the Drude-Smith model. The electron mobility of the InN film is 1217±58cm2∕Vs, while that of the InN nanorods is 80±5cm2∕Vs. The reduced mobility of carriers for the latter can be attributed to the restricted carrier transport within the nanorods.