Search

© 2017 Author(s). Co-doping with fluorine is a potentially promising method for defect passivation to increase the donor electrical activation in highly doped n-type germanium. However, regular high dose donor-fluorine co-implants, followed by conventional thermal treatment of the germanium, typically result in a dramatic loss of the fluorine, as a result of the extremely large diffusivity at elevated temperatures, partly mediated by the solid phase epitaxial regrowth. To circumvent this problem, we propose and experimentally demonstrate two non-amorphizing co-implantation methods; one involving consecutive, low dose fluorine implants, intertwined with rapid thermal annealing and the second, involving heating of the target wafer during implantation. Our study confirms that the fluorine solubility in germanium is defect-mediated and we reveal the extent to which both of these strategies can be effective in retaining large fractions of both the implanted fluorine and, critically, phosphorus donors.

Recently, sub-10-nm-diameter InGaAs vertical nanowire (VNW) MOSFETs have been demonstrated. The key to this achievement was the use of Ni for the top ohmic contact. In this paper, we present a detailed study of the impact of Ni and Mo contacts on the electrical characteristics of highly scaled InGaAs VNW MOSFETs. Sequential annealing experiments are presented that reveal the optimum temperature for each type of contact. A negative temperature dependence of the ON-resistance of 7-nm-diameter Ni-contacted devices suggests the existence of an energy barrier. We also observe an unexpected transconductance and drain-induced barrier loweirng (DIBL) dependence on transistor diameter in Ni-contacted devices as well as abnormal DIBL asymmetry to swapping source and drain. All these results can be explained by Ni diffusing down the nanowire during the contact annealing process, reducing the effective channel length, and creating a Schottky-barrier drain.

Thesis: Ph. D., Massachusetts Institute of Technology, Department of Materials Science and Engineering, 2017., This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections., Cataloged from student-submitted PDF version of thesis., Includes bibliographical references (pages 129-140)., GaAs-based transistors are capable of operating at high frequency with low noise, and are produced in large volumes for a wide range of applications including microwave frequency ICs for input/output in mobile devices. However, Si CMOS still holds an advantage for digital logic due to wide market penetration resulting in decades of development and lower cost. Monolithic integration of III-V analog circuity and Si CMOS gives circuit designers the best of both materials. In addition, by substituting GaAsxP₁-x (0.8 < x < 1) for GaAs as an active material, we can take advantage of its higher breakdown voltage and reduced lattice mismatch with Si. In this thesis, we study GaAsP/InGaP heterojunction bipolar transistors (HBTs) grown via MOCVD as a test-bed for III-V microelectronics integration with Si. Epitaxial challenges involving growth of GaAsP/InGaP HBT structures on Si substrates were addressed. Heavy C p-type doping of GaAsP via MOCVD, necessary for the HBT base region, was studied. Growth rate, composition, and hole concentration dependence on C precursor (CBrCl₃) input was investigated, yielding GaAsP films with hole concentrations in excess of 2 x 10¹⁹ cm-³. GaAs₀₈₂₅P was grown on Si substrates via a SiGe graded buffer with a threading dislocation density of 3.7 x 106 cm-2 measured by PV-TEM and EBIC. This density is appropriate for fabrication of minority-carrier devices such as HBTs. GaAsP/InGaP HBTs were fabricated on both GaAs and Si substrates with a range of defect densities to measure the effect on DC performance and prove the feasibility of GaAsP transistor growth on Si. Models for the effect of threading dislocation density and misfit dislocation density (in the active device layers) on current gain were developed. A GaAsP/InGaP HBT grown on Si was demonstrated with a current gain as high as 158. Changes in GaAsxP₁-x composition from 0.825 < x < 1 did not have a significant effect on current gain. Collector current was determined not to be controlled by, by Christopher Heidelberger., Ph. D.

CBrCl₃ is shown to be a useful precursor for heavy p-type carbon doping of GaAsxP1−x grown via metalorganic chemical vapor deposition (MOCVD) across a range of compositions. Structural and electrical properties of the GaAsP films were measured for various processing conditions. Use of CBrCl3 decreased the growth rate of GaAsP by up to 32% and decreases x by up to 0.025. The dependence of these effects on precursor inputs is investigated, allowing C-doped GaAsP films to be grown with good thickness and compositional control. Hole concentrations of greater than 2×10¹⁹ cm−3 were measured for values of x from 0.76 to 0.90., National Science Foundation (U.S.) (Award 0939514), National Research Foundation of Singapore, National Science Foundation (U.S.) (Award DMR-14-19807)