Research of Si-ZnO Thin-Film Transistors Deposited by Atomic Layer Deposition

Si-ZnO thin-film transistors were fabricated using atomic layer deposition (ALD) then annealed in oxygen at 400°C for 1 hour and are demonstrated. Hexagonal wurtzite structure for ZnO was presented in all films, with a primary diffracted peak in the (100) direction regardless of the annealing treatment. First-principle density functional theory (DFT) calculations supported the observed crystalline characteristics. Electrical characteristics were improved with Si doping, increasing carrier concentration to <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" id="M1"> <a:mn>3.51</a:mn> <a:mo>×</a:mo> <a:msup> <a:mrow> <a:mn>10</a:mn> </a:mrow> <a:mrow> <a:mn>20</a:mn> </a:mrow> </a:msup> <a:mtext> </a:mtext> <a:mtext>c</a:mtext> <a:msup> <a:mrow> <a:mtext>m</a:mtext> </a:mrow> <a:mrow> <a:mo>−</a:mo> <a:mn>3</a:mn> </a:mrow> </a:msup> </a:math> and reducing film resistivity to <c:math xmlns:c="http://www.w3.org/1998/Math/MathML" id="M2"> <c:mn>0.28</c:mn> <c:mo>×</c:mo> <c:msup> <c:mrow> <c:mn>10</c:mn> </c:mrow> <c:mrow> <c:mo>−</c:mo> <c:mn>1</c:mn> </c:mrow> </c:msup> <c:mtext> </c:mtext> <c:mi>Ω</c:mi> <c:mo>.</c:mo> <c:mtext>cm</c:mtext> </c:math> with well-matched optical bandgap widening from UV-vis results using Tauc plot: Burstein-Moss (BM) effects. After implementing the oxygen ambient annealing and Si doping, the device parameters to realize the low power/energy consumption were improved to an SS value of 0.67 V/decade; threshold voltage ( <e:math xmlns:e="http://www.w3.org/1998/Math/MathML" id="M3"> <e:msub> <e:mrow> <e:mi>V</e:mi> </e:mrow> <e:mrow> <e:mtext>th</e:mtext> </e:mrow> </e:msub> </e:math> ) of 0.68 V; and a field effect mobility ( <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" id="M4"> <g:msub> <g:mrow> <g:mi>μ</g:mi> </g:mrow> <g:mrow> <g:mtext>FE</g:mtext> </g:mrow> </g:msub> </g:math> ) of 5.22 cm2/V·s, respectively. The improved device parameters were related to the reduced interface trap densities due to annealing passivated oxygen vacancies, and the BM effect induced percolation conduction with increased carrier concentration due to Si doping, respectively. Thus, incorporating Si-based ZnO materials by ALD offers a viable candidate for superior device characteristics for energy-saving appliances.