Laurence P. Sadwick

Quantitative scanning capacitance microscopy analysis of two-dimensional dopant concentrations at nanoscale dimensions

We have applied the scanning capacitance microscopy (SCM) technique of twodimensional (2-D) semiconductor dopant profiling to implanted silicon cross sections. This has permitted the first direct comparison of SCM profiling scans to secondary ion mass spectroscopy (SIMS) depth profiles. The results compare favorably in depth and several readily identifiable features of the SIMS profiles such as peak concentration and junction depth are apparent in the SCM scans at corresponding depths. The application of dopant profiling to two dimensions is possible by calibrating the SCM levels with the one-dimensional (1-D) SIMS data. Furthermore, we have subsequently simulated the SCM results with an analytic expression readily derivable from 1-D capacitance vs voltage capacitance-voltage theory. This result represents a significant breakthrough in the quantitative measurement of 2-D doping profiles.

Effect of rapid thermal annealing on planar‐doped pseudomorphic InGaAs high electron mobility transistor structures

We have investigated the effects of rapid thermal annealing on the electrical and optical properties of planar‐doped AlGaAs/InGaAs/GaAs high electron mobility transistor structures grown by molecular beam epitaxy. Hall effect and photoluminescence measurements on samples with In0.22Ga0.78As and In0.28Ga0.72As channels reveal a temperature‐dependent degradation in sheet charge density, Hall mobility, and photoluminescence response. The structures were essentially stable through the temperature range used in normal device processing. However, annealing temperatures greater than 700 °C resulted in strain relaxation and layer intermixing, especially for the In0.28Ga0.72As sample.

Device and material properties of pseudomorphic HEMT structures subjected to rapid thermal annealing

The device-related effects of rapid thermal annealing (RTA) on the electrical and optical properties of planar-doped AlGaAs/InGaAs/GaAs high-electron-mobility transistor structures grown by molecular beam epitaxy were investigated. Specifically, electrical and optical characterization techniques such as capacitance versus voltage, current versus voltage, Hall effect, and photoluminescence have been applied to study the effects that typical III-V compound semiconductor rapid thermal processes (RTPs) have on the properties of pseudomorphic AlGaAs/InGaAs/GaAs structures for two different values of In mole fraction content. The effect and stability of the indium mole fraction on both heterostructure and device integrity with respect to RTA schedule has been investigated in detail. >

A comparison of the reactions of phosphorus precursors on deposited GaP and InP films

The reactions of the phosphorus precursors tertiarybutylphosphine (TBP), tris(dimethylamino)phosphorus (TDMAP), and tertiarybutylbis(dimethylamino) phosphine (TBBDMAP) on deposited GaP and InP films have been compared in low-pressure conditions. The rates of decomposition are generally greater on GaP than on InP and correlate well with the reported growth results for chemical beam epitaxy (CBE). Those phosphorus precursors that can be used for epitaxial growth without precracking have the highest heterogeneous reaction rates. The differences in apparent activation energies suggest that these compounds adsorb more strongly on GaP than on InP surfaces.

Tris-dimethylaminophosphorus reactions at low pressure on GaP, InP and quartz surfaces

Abstract The decomposition of the phosphorus precursor tris-dimethylaminophosphorus (TDMAP) at low pressures (∼ 10 −4 Torr) has been studied by mass spectrometry. Three different surfaces were used: quartz, InP and GaP. For the three surfaces pyrolysis is 50% complete at approximately 820, 520 and 350°C, respectively. The activation energy for decomposition on the GaP surface is 18.5 ± 2.5 kcal/mol and for the quartz surface, 47.3 ± 3.5 kcal/mol. The principle reaction products are dimethylamine, methylmethyleneimine and methyleneimine. On the quartz surface decomposition appears to occur via homolysis of the parent molecule, producing dimethylaminyl radicals, which react subsequently to form the observed products. For the surface-catalyzed reactions an intramolecular reaction mechanism is proposed in which there is a transfer of a hydrogen atom from a methyl group to the nitrogen lone-pair on an adjacent ligand. This reaction would produce both dimethylamine and methylmethyleneimine.

Enhancement of high-temperature high-frequency performance of GaAs-based FETs by the high-temperature electronic technique

This paper reports the effects of high temperature on high-frequency/high-speed field effect transistors (FETs), particularly GaAs-based MESFETs and HEMTs. The high-temperature electronic technique (HTET) was employed to stabilize and improve the performance of these devices at high temperatures. This work focuses on detailed high-temperature experiments of high-frequency scattering parameters of various transistors. Comparable gain level to that obtained at room temperature was achieved at elevated temperature through the use of the HTET.

Pyrolysis of tertiarybutylphosphine at low pressure

The pyrolysis of tertiarybutylphosphine (TBP) has been studied in the low pressure conditions used for chemical beam epitaxy (CBE). The pyrolysis studies were carried out in low pressure reactors of two different configurations, one of which is a cracker cell designed for use in a CBE system. The reaction products were studied using a quadrupole mass spectrometer. The products observed are accounted for by a reaction mechanism involving homolysis of the parent TBP molecule to produce PH2 and C4H9 radicals. These undergo subsequent reactions to form the stable products C4H8, PH3 and H2, with smaller amounts of P and P2 being produced. The production of the sub-hydride PH2 using this cracker cell design indicates that the use of partially cracked TBP may be a promising technique for reducing the amount of carbon incorporated into the growing epitaxial layer.

Chemical beam epitaxy of InP without precracking using tertiarybutylbis(dimethylamino)phosphine

Abstract For the first time, single crystalline layers of indium phosphide (InP) have been grown by the chemical beam epitaxy (CBE) technique without thermally precracking the phosphorus (P) source. This was accomplished using a novel P precursor, tertiarybutylbis(dimethylamino)phosphine (TBBDMAP). For a constant input V III ratio of 7.2, InP growth was studied for growth temperatures from 450 to 530°C. At 450°C, the surface was indium rich due to the incomplete pyrolysis of TBBDMAP. At 480 and 510°C, InP epilayers were successfully grown without precracking the TBBDMAP. An indium-rich surface was also observed at 530°C using this input V III ratio due to the high rate of phosphorus desorption. At growth temperatures of 480 and 510°C, the effect of the cracker cell temperature on the InP growth rate was studied.

CBE growth of InP using BPE and TBP: a comparative study

Abstract Results of a comparative study on the growth of indium phosphide (InP) by chemical beam epitaxy (CBE) using two alternative phosphorous (P)-precursors, bisphosphinoethane (BPE) and tertiarybutylphosphine (TBP), are presented. For both P-precursors, ethyldimethylindium (EDMIn) was used as the indium (In) precursor. TBP has gained wide acceptance in gas phase growth techniques such as organometallic vapor phase epitaxy (OMVPE) and CBE and its variants. However, BPE has not been extensively applied to CBE growth with only preliminary results of CBE-grown InP using BPE having been published to date. This paper presents the first systematic study on the growth rate and efficiency, morphology, electrical and optical properties of CBE-grown InP using BPE. We compare these results to data obtained for CBE-grown InP using TBP. To make this comparison more meaningful, all TBP and BPE growth runs were performed in sequence using the same CBE hardware under identical experimental conditions. Duplicate sets of sample runs were grown to verify reproducibility. Details of the effects of substrate temperature, cracker cell temperature and V III ratio on the electrical transport properties determined from 77 K and room-temperature Hall measurements and the optical properties characterized by 14 K photoluminescence (PL) measurements are presented. The Hall carrier concentrations and PL data strongly correlate with the sulfur impurity levels measured by secondary ion mass spectroscopy (SIMS). All of the undoped InP epitaxial layers show n-type conductivity. Striking similarities in the electrical and optical properties of InP grown using either BPE or TBP were observed indicating that BPE and TBP, in many respects, can be viewed as interchangeable P-sources.

Thermal currents in proton isolated gallium arsenide structures at elevated temperatures

Using a new and simple technique, thermal currents between proton isolated devices fabricated on semi‐insulating gallium arsenide (GaAs) substrates have been observed for the first time at temperatures from 25 °C up to 300 °C. The thermal currents show definite Ohmic behavior with respect to the applied voltage at a fixed temperature. An Arrenhius plot of the thermal current at a fixed bias voltage level for a given test structure yields a straight line with an activation energy that can be ascribed to known deep levels in GaAs. The implications that this thermal leakage current have on the functionality of GaAs metal‐semiconductor field‐effect transistors at high temperatures are also addressed in this work.