Three Essays in Macroeconomics

The scope of the dissertation is: broadly-defined) general macroeconomics. The first essay is on optimal taxation and capital structure, the second essay is on firm dynamics, and the third essay is on financial crises. The first essay clarifies the role of the corporate income tax: as a form of double taxation) for achieving socially optimal allocations in the Mirrlees framework when the government cannot tax unrealized capital income at the individual level. Use of the corporate tax requires changes in the individual capital tax. The novelty of the paper is that the sophisticated tax system is designed to influence the individual agent\u27s portfolio choice of debt and equity, which in turn endogenizes the leverage ratio. The optimum corporate tax is indeterminate, but a minimal level is ecessary. An immediate question is what happens to capital structure if we increase or decrease the level of the corporate tax. Surprisingly, unlike in classical capital structure theories, in this optimal tax mechanism, the firm\u27s leverage ratio is independent of the corporate tax rate. The second essay examines firm dynamics to explain the following empirical facts:: i) The size of a firm and its growth rate are negatively correlated;: ii) but, they are often independent for firms above a certain size. Existing theories of firm dynamics can explain the first fact, but cannot explain the second. This paper studies a dynamic moral hazard problem under an AK-technology. In a first best world, the expected growth rate is strictly decreasing with capital. However, with information asymmetry our theory is consistent with both empirical facts because the optimal contract dictates under-investment in low-level capital states and over-investment in high-level capital states. The reason is that the given convex production technology becomes nonconvex in equilibrium due to the information asymmetry and the degree of the nonconvexity differs by the level of capital. We also fully characterize the agent\u27s incentives. The capital accumulation mechanism induces incentive schemes that are different from optimal contracts in the literature on principal-agent models. Finally, in the third essay - This essay is a joint work with Costas Azariadis - we propose a model of financial crises as transitions from an efficient and unstable state to an inefficient and stable state in a simple economy with sector-specific shocks. The main driving force of this transition is the unwinding of unsecured loans. Introducing public debt increases the volatility of stock prices. We also discuss possible policy interventions

Determination of energy levels of surface states in GaAs metal-semiconductor field-effect transistor using deep-level transient spectroscopy

The energy levels of surface states at the surface of GaAs were determined through capacitance deep-level transient spectroscopy of GaAs metal-semiconductor field-effect transistor with large gate periphery. Two types of hole-like traps are observed in the spectra. These originate from the surface states at the ungated regions between gate and source/drain electrodes. The activation energies of both surface states are determined to be 0.65 +/- 0.07 and 0.88 +/- 0.04 eV, which agree well with the energy levels of As-Ga(+) and As-Ga(++) within band gap of GaAs, responsible for the Fermi level pinning at the surface.open151

Determination of energy levels of surface states in GaAs metal-semiconductor field-effect transistor using deep-level transient spectroscopy

The energy levels of surface states at the surface of GaAs were determined through capacitance deep-level transient spectroscopy of GaAs metal-semiconductor field-effect transistor with large gate periphery. Two types of hole-like traps are observed in the spectra. These originate from the surface states at the ungated regions between gate and source/drain electrodes. The activation energies of both surface states are determined to be 0.65 +/- 0.07 and 0.88 +/- 0.04 eV, which agree well with the energy levels of As-Ga(+) and As-Ga(++) within band gap of GaAs, responsible for the Fermi level pinning at the surface.open151

Evolution of optical phonons in CdS nanowires, nanobelts, and nanosheets

We report Raman scattering from single and ensemble CdS nanowires, nanobelts, and nanosheets. The Raman spectra of nanobelts and nanosheets are notably different from those of nanowires, exhibiting a strong enhancement of the multiphonon response. Moreover, the first-order longitudinal optical (LO) phonon energy systematically increases with increasing lateral size from nanowires to nanobelts, and to nanosheets. These results suggest that the optical phonons in the CdS nanostructures are influenced by strain, crystallinity, and exciton-LO phonon coupling.open342

Effects of deep levels on transconductance dispersion in AlGaAs/InGaAs pseudomorphic high electron mobility transistor

The effects of deep levels on the transconductance dispersion in an AlGaAs/InGaAs pseudomorphic high electron mobility transistor was interpreted using capacitance deep level transient spectroscopy (DLTS). Transconductance was decreased by 10% in the frequency range of 10 Hz-10 kHz at the negative gate bias, but it was increased at the positive one. In the DLTS spectra, two hole trap-like signals corresponding to surface states were only observed at the negative pulse bias, whereas the DX-center with the activation energy of 0.42 +/- 0.01 eV were observed at the positive one. The activation energy agrees well with that obtained from the temperature dependence of the positive transconductance dispersion, 0.39 +/- 0.03 eV. These provide evidence that the positive and negative transconductance dispersions are due to the DX center and surface states, respectively.open9

The EQIP GIS, Web-based Decision Program

Working together, NRCS and Purdue University staff developed a GIS, web-based EQIP decision program. Landowners and NRCS personnel enter required EQIP information via a mapping service. Other subroutines store the information for use by NRCS in ranking and funding EQIP applications that receive the highest scores subject to budget constraints.Research and Development/Tech Change/Emerging Technologies,

Observation of inductively coupled-plasma-induced damage on n-type GaN using deep-level transient spectroscopy

The effects of inductively coupled plasma (ICP) etching on electrical properties of n-type GaN Schottky contacts were investigated by observing ion damage using deep-level transient spectroscopy. An electron trap, not previously seen, localized near the contact, as well as a pre-existing trap, was observed in the ICP-etched sample. The ICP-etched surface was found to be N-deficient, which means that N vacancies (V-N) were produced by ICP etching. From these, the origin of the ICP-induced electron trap was suggested to be V-N or a V-N-related complex of point defects. The ICP-induced traps provided a path for the transport of electrons, leading to the reduction of Schottky barrier height and increase of gate leakage current.open273