Van der Pauw method

About: Van der Pauw method is a research topic. Over the lifetime, 1682 publications have been published within this topic receiving 25364 citations.

Molecular beam epitaxial growth and characterization of lead telluride for laser diodes

Abstract: The characteristics of PbTe films grown by molecular beam epitaxy (MBE) have been investigated. These films were grown on (100) oriented Tl-doped PbTe substrates under UHV conditions (~5×l0−9 Torr during deposition). Substrate surface contamination levels were studied with Auger electron spectroscopy. Oxygen, the dominant impurity observed, is rapidly thermally desorbed from PbTe, but is stable on Pb1−xSnxTe up to at least 410°C. Carrier concentration and mobility were measured with the Van der Pauw technique. The electron mobility increased strongly with increasing film thickness, varying from 4,000 to 14,000 cm2/volt-sec as the thickness increased from 2.0 to 7.3 µn. The film surface also became smoother with increasing film thickness. These results suggest the need for a buffer layer in a laser structure. Lasers grown with 6 μm thick buffer layers have exhibited extremely low threshold current densities (40 A/cm2 at 13 K) and very high junction resistancearea products at zero-bias (0.7 Ω−cm2 at 77 K), indicative of very high junction quality.

Space-charge controlled conduction in low-temperature-grown molecular-beam epitaxial GaAs

Abstract: Current transport in low-temperature (LT) molecular-beam epitaxial GaAs grown at 200-300 °C on an n+ GaAs substrate is studied by means of current–voltage–temperature characteristics. The resistivity of LT GaAs at low electric fields is ρ⩾108 Ω cm, much higher than resulting from van der Pauw measurements. It is found that the measured resistivity decreases with increasing the LT GaAs thickness. This is explained by space-charge effect in the vicinity of n+/LT GaAs junction and subsequent suppression of hopping conduction in the high-field junction region.

Thin film thermoelectric characterization techniques

Abstract: The key thin film thermoelectric characterization techniques are described. Due to the small dimensions, a careful examination of electrical and thermal paths in the device is necessary. We describe both in-plane and cross-plane measurement methodologies. Sample requirements for four-probe and van der Pauw methods for in-plane electrical conductivity measurement are discussed. The in-plane Seebeck coefficient is characterized under a temperature gradient which generates a voltage. Precise measurements of temperature and voltage at the same location in the sample are very important. For the cross-plane electrical conductivity, the modified transmission line method is evaluated. To eliminate parasitic contact and substrate resistances, several samples with varying thicknesses are required. Two approaches, a DC method and the 3ω method, are described in detail for the cross-plane Seebeck coefficient characterization. Next, we focus on the transient Harman method to directly measure the cross-plane thermoelectric figure of merit of a thin film. The device requirements for reducing parasitic heat losses and current nonuniformity are presented. Thermoreflectance imaging can be used together with transient Harman in order to extract electrical and thermal conductivities and the Seebeck coefficient simultaneously. Finally, Z-meters are described for directly determining the figure of merit and efficiency of a thermoelectric element or module under a large temperature gradient. Recent developments have significantly reduced thermal and electrical parasitics, as well as radiation heat loss in the system, enabling ZT measurement of legs as thin as one hundred microns.

Open tube diffusion of Zn into AlGaAs and GaAs

Abstract: A new method of open tube zinc diffusion into AlGaAs and GaAs using a confined chamber has been developed. The depth and quality of Zn diffusion into GaAs and AlxGa1−xAs (0.1≤x≤0.5) at 700 °C, are compared with the traditional closed tube diffusion process. It is seen that the new process provides for a very well controlled diffusion depth and allows shallow diffusion. The specific resistivity and surface carrier concentration are measured by the Van der Pauw method. The diffusion quality is affected by the choice of solvent metals. Some variations of solvent metals are discussed. This technique is used for improvement of ohmic contacts in monolithic integrated‐optical devices.