Hongqiang Lu

Electrical characteristics of magnesium-doped gallium nitride junction diodes

Electrical characteristics of lateral p+n diodes made from gallium nitride epitaxial layers on sapphire substrates are reported. The current–voltage characteristics are observed to have several distinct regions in which a tunneling current has been identified at low forward bias in addition to the conventional temperature-dependent diffusion current observed at moderate forward bias. A tunneling behavior indicates the presence of deep-level traps at the junction, which alter the electrical behavior of these junctions compared to the conventional behavior. In addition, space-charge-limited currents are found to influence these junctions at large forward and reverse bias.

Electrical characterization of Mg‐doped GaN grown by metalorganic vapor phase epitaxy

We have applied frequency‐dependent capacitance measurements and admittance spectroscopy on GaN:Mg to study the electronic states associated with Mg doping. Metalorganic vapor phase epitaxy GaN:Mg samples with two different Mg doping levels were grown and thermally annealed in nitrogen. Lateral dot‐and‐ring Schottky diodes using Au/Ti were fabricated. Frequency‐dependent measurements on these diodes show that the capacitance is reduced at a higher frequency, most likely due to the inability of a deep center to maintain an equilibrium ionization state under a high‐frequency modulation. Admittance spectroscopy, in which the conductance is monitored as a function of temperature, verifies the existence of one impurity‐related acceptor level in the higher Mg‐doped sample with an activation energy of 136 meV. For the lower Mg‐doped sample, two acceptor levels at 124 and 160 meV were observed. We believe these levels are most probably associated with the Mg acceptor state itself, possessing energy levels which a...

Photoassisted anodic etching of gallium nitride

The first study of photo-assisted anodic etching of unintentionally doped n-GaN at room temperature is reported here. The electrolyte used is a mixture of buffered aqueous solution of tartaric acid and ethylene glycol. The etching rate varies from {approximately}20 {angstrom}/min to as high as 1600 {angstrom}/min. A systematic study shows that (1) the etch rate, as well as the surface roughness, increases with the current density; (2) the etching rate is the highest when the pH of the electrolyte is {approximately}7; and (3) the etching is faster when there is more ethylene glycol in the electrolyte solution. Ga-N-based III-V nitrides are important candidates for applications in blue light emitters and lasers, high voltage and high temperature electronics.

Copper drift in methyl-doped silicon oxide film

Drift of copper (Cu) ions into methyl-doped silicon oxide film, a promising low-dielectric-constant (low-κ) material for inter-layer dielectrics applications in ultralarge scale integrated circuit (ULSI) interconnects, was investigated using bias temperature stressing (BTS)/capacitance–voltage (C–V), current–voltage (I–V) at elevated temperatures and time-dependent dielectrics breakdown (TDDB) tests. Standard and control metal–insulator–semiconductor capacitor test samples with “sandwich” dielectric layer structures were used in the tests. BTS in nitrogen (N2) ambient at an electric field magnitude up to 1.5 MV/cm and with temperatures between 175 and 275u2009°C was used to accelerate the Cu ion drift. By studying flat band voltage shift in C–V tests, leakage current magnitude in I–V tests and time to fail in TDDB tests, it is demonstrated that Cu ions readily drift into methyl-doped silicon oxide under electric fields at elevated temperatures. Results obtained using different techniques correlate well to eac...

Reactive ion etching of GaN in BCl{sub 3}/N{sub 2} plasmas

The etching of gallium nitride by reactive ion etching has been investigated to determine the effect of the addition of nitrogen to boron trichloride plasmas. The etch rate and dc bias are monitored while the reactor parameters are systematically varied. The experimental results indicate that the etch rate of GaN is enhanced when nitrogen is added to BCl 3 plasmas. Surface analysis by x-ray photoemission spectroscopy and electron microscopy indicate that there is little etch induced damage. The etch rate of sapphire has also been studied and is found to decrease with nitrogen addition allowing the GaN/sapphire selectivity to be enhanced with added nitrogen.

Chemical Mechanical Polishing of Low Dielectric Constant Oxide Films Deposited Using Flowfill Chemical Vapor Deposition Technology

In this work, the properties and chemical mechanical polishing (CMP) characteristics of thin films of a new low dielectric constant (low-κ) oxide deposited using Flowfill chemical vapor deposition (CVD) technology are presented. This oxide film consists of silicon dioxide network with methyl groups incorporated and has a dielectric constant K as low as ∼2.7. The film properties were studied using Fourier transform infrared spectroscopy (FTIR), spectroscopic ellipsometry, Rutherford backscattering, atomic force microscopy, and capacitance-voltage measurements. The refractive index, as low as 1.38, was measured using spectroscopic ellipsometry. The surface was found to be more hydrophobic compared to conventional CVD oxide. The stretching mode of the Si-O bond peak in the FTIR spectrum shifts to lower wavenumber, which corresponds to lower Si-O bonding energy, with increase in the methyl concentration inside the film. The CMP removal rate decreases as the methyl concentration in the film increases. An atomically smooth surface with root mean square surface roughness <1 nm over an area 2 X 2 μm was obtained after CMP. Our results suggest that the incorporation of methyl groups results in a reduction in the CMP removal rate. We speculate that the diffusion of water into the film is probably the CMP removal rate-limiting step.

Characterization of methyl-doped silicon oxide film deposited using Flowfill™ chemical vapor deposition technology

In this article, methyl-doped silicon oxide films deposited using Flowfill™ chemical vapor deposition (CVD) technology have been chracterized for use in inter-layer dielectrics application. Films with different methyl concentrations were deposited and characterized in order to study the effect of methyl concentration on film properties. Material properties including chemical composition and bonding structure, density, dielectric constant (κ), refractive index, thermal stability, resistance to moisture absorption, leakage current, and hardness were investigated. The films have a κ as low as 2.7 and were found to be thermally stable up to 550u200a°C. They show excellent resistance to moisture absorption. Low-leakage current and breakdown voltage higher than 3 MV/cm were obtained. Their hardness is lower than silicon oxide deposited using plasma-enhanced CVD but is higher than most polymer and nanoporous low-dielectric constant (low-κ) materials. The chemical mechanical polishing (CMP) characteristics of these f...

MOCVD Growth of GaN on bulk AlN Substrates

In this paper, the growth of epitaxial GaN layers on c-plane and a-plane bulk AIN substrates by metalorganic vapor phase epitaxy is reported. The AlN boules were grown by the sublimationrecondensation technique. Single crystal GaN films grown on the c-plane orientation replicate the substrate orientation. However the surface of the epilayer had a high density of cross-hatch defect lines, presumably caused by mechanical polishing damage. The low temperature PL spectra of these films were dominated by exciton emission at 3.470 eV with a FWHM of 14 meV at 7 K. On the other hand, GaN grown on the a-plane orientation AlN was polycrystalline and the surface was rough with ridge-like facets. The PL from this film showed a dominate peak at 3.406 eV which may originate from defect-bound excitons. The quality of the GaN layers grown on these AIN bulk substrates appeared to be limited by the surface preparation method, which has not been optimized.

Characterization of methyl-doped silicon oxide film for inter-layer dielectrics application

In this work, methyl-doped silicon oxide films deposited using Flowfill/sup TM/ chemical vapor deposition (CVD) have been characterized for use in inter-layer dielectrics (ILD) application. Films with different methyl contents were studied to understand the effects of incorporated methyl groups on the properties. Chemical composition and bonding structure, dielectric constant (k), refractive index (RI), density, thermal stability, moisture permeability, and hardness were investigated. Chemical mechanical polishing (CMP) of these films and their stability under O/sub 2/, N/sub 2/ and H/sub 2/ plasma treatments were also studied.