George N. Maracas

In situ spectroscopic ellipsometry in molecular beam epitaxy

Noninvasive, real‐time material growth monitoring is becoming increasingly important as epitaxial layer structures become more complex and the thickness and alloy composition tolerances are reduced. The technique of spectroscopic ellipsometry has been adapted to a commercial III–V semiconductor molecular beam epitaxy (MBE) system to monitor layer thickness, ternary alloy composition, and substrate temperature in real time during the growth of multilayer structures. Practical system considerations for reliably implementing the rotating analyzer ellipsometer in a hydride source MBE environment that contains a high pressure of dimeric group V species will be discussed. Measurement of substrate temperature from room temperature to typical growth temperatures will then be presented as well as in situ determination of alloy composition and thickness for efficient growth calibration. A growth run of GaAs/AlGaAs epitaxial layers will be examined to observe surface smoothing upon group III pulse deposition and gro...

Measurement of GaAs temperature‐dependent optical constants by spectroscopic ellipsometry

Temperature‐dependent optical constants (30 °C<T<650 °C) of semi‐insulating GaAs in the range of 1.24–5.00 eV were measured using spectroscopic ellipsometry (SE) inside a specially designed molecular beam epitaxy chamber. Because of the lack of native oxides and surface adsorbates, a simple two‐phase model (vacuum/substrate) could be used to calculate optical constants from the ellipsometry data. A Lorentz oscillator model with seven oscillators was used to fit the e1 and e2 experimental data to determine the temperature‐dependent interband transition energies, E1 and E1+Δ1. Changes in the dielectric function at different surface temperatures would allow SE to be used as a tool to accurately measure the surface temperature of GaAs. Accurate knowledge of the temperature‐dependent optical constants is also useful for the design of optical devices.

Reduction of the thermal impedance of vertical‐cavity surface‐emitting lasers after integration with copper substrates

Vertical‐cavity surface‐emitting lasers (VCSELs) have been transferred from their original GaAs substrates to Cu substrates and continuous wave operation has been obtained on the VCSELs after epitaxial transfer. The resultant measurements show a doubling of the output power and a 20% reduction in the thermal impedance. Increased optical power is explained by improved thermal heat sinking as measured from the lasing spectra of horizontal‐cavity edge‐emitting lasers fabricated from the same VCSEL material.

A vertical-cavity surface-emitting laser appliqued to a 0.8-μm NMOS driver

An optoelectronic integrated circuit (OEIC) composed of a vertical-cavity surface-emitting laser (VCSEL) appliqued to an NMOS drive circuit was fabricated to form an optical link from the CMOS chip. A custom NMOS circuit was designed and fabricated through the MOSIS foundry service in a standard 0.8-/spl mu/m CMOS process. InGaAs quantum-well VCSELs were grown, fabricated and tested on an n-type GaAs substrate. Next, the VCSELs underwent a substrate removal technique and were appliqued to the NMOS circuitry. The OEIC was tested at the chip level and showed an electrical to optical conversion efficiency of 1.09 mW/V. Modulation results are also discussed.

Ellipsometry for III–V epitaxial growth diagnostics

Spectroscopic ellipsometry’s (SE’s) strength as an in situ semiconductor crystal growth process diagnostic lies in the fact that the material’s dielectric properties (pseudodielectric functions) are dependent upon temperature and alloy composition. These dependencies can be exploited to monitor and control epitaxial growth in real time. This article reviews several aspects of growth and control of III–V semiconductors grown at Arizona State University by molecular beam epitaxy (MBE) using SE. Chamber and manipulator design considerations for implementing SE on a MBE and a gas source MBE with substrate rotation will first be discussed. A commercially available ‘‘ellipsometer‐ready’’ MBE system will then be described. It will then be shown that a MBE process can be established without conventional analysis tools such as reflection high energy electron diffraction. Measurement and control of substrate temperature by SE will be shown. This is possible by using the temperature‐dependent pseudodielectric functi...

X-band heterostructure interband tunneling FET (HITFET) VCOs

This paper reports on the DC and microwave performance of novel X-band voltage controlled oscillators fabricated by integrating heterostructure interband tunneling diode (HITD) with a heterostructure FET. The measured RF performance of VCOs incorporating single and double HITDs is discussed. The power output of the single HITD VCO was 2.0 dBm and that of the dual HITD was 4.3 dBm at a center frequency of 8.2 GHz. The dual HITD VCO also exhibited a wider tuning range than the single HITD VCO. The phase noise of these VCOs was approximately -128 dBc, 3 MHz away from the center frequency.

Microfabrication of two layer structures of electrically isolated wires using self-assembly to guide the deposition of insulating organic polymer

Abstract The fabrication of two layer structures of electrically isolated wire — crossed wire structures and a surface coil inductor — is described. The fabrication process utilizes the tools of soft lithography and incorporates two levels of self-assembly. The use of microcontact printing and patterned self-assembly of liquid polymers removes the need for registration of the insulating layer with the underlying layer as required in conventional lithography techniques. The performance characteristics of the surface coil inductor are measured and closely resemble those predicted by theory.

DETERMINATION OF MOLECULAR BEAM EPITAXIAL GROWTH PARAMETERS BY ELLIPSOMETRY

The use of ellipsometry as an alternative technique for in situ determination of molecular beam epitaxial growth parameters has been demonstrated. Epitaxial growth has been monitored in real time using three discrete wavelengths to extract growth rates and alloy composition. The effect of substrate rotation on the measured growth rates has also been determined by this technique. From measurements of the GaAs growth rates versus substrate temperature, a value of 4.68±0.12 eV for the activation energy for Ga desorption during GaAs growth was obtained. This agrees with values obtained by other measurement techniques.

Low loss air-gap spiral inductors for MMICs using glass microbump bonding technique

Air-gap spiral inductor structures have been fabricated and itegrated with semiconductor substrates using glass microbump bonding (GMBB) techniques. Spiral inductors using air-gap structures have the advantages of low losses, and low parasitic capacitance compared to conventional inductors on doped silicon semiconductor substrate. Stacked air-gap spiral inductors on GaAs substrates using GMBB techniques also can reduce the inductor area. Because the glass microbump bonding techniques are simple, this bonding technique provides an alternative integration approach for monolithic microwave integrated circuits (MMICs). Experimental results of air-gap spiral inductor on both silicon and GaAs substrates are presented in this paper.

Ex situ ellipsometry characterization of excimer laser annealed amorphous silicon thin films grown by low pressure chemical vapor deposition

Spectroscopic ellipsometry was used to monitor excimer laser annealed thin (∼100 nm) amorphous silicon (a-Si) films grown on quartz substrates by low pressure chemical vapor deposition (LPCVD). The peak position of the imaginary part of the complex dielectric function e2 was used to determine the degree of crystallization of the a-Si. The amplitude of e2 at the Si E1 transition energy is found to be a good indicator of the polycrystalline silicon (poly-Si) grain size after laser annealing with good correlation between ex situ ellipsometric data and poly-Si grain sizes being observed. Spectroscopic ellipsometry provides a contactless, nondestructive, and simple technique for monitoring laser annealing both in situ during the annealing process or ex situ after annealing.