Considering this question, actually I not remember as I must straighten square root symbol to have the classic sqrt symbol. I have used (for example),
\def\mySqrt{\radical"0270373\relax}
but it not works. I not remember if I must to use \mathstrut, \smash or other....
\documentclass[a4paper,12pt]{article}
\usepackage{amsmath,amssymb}
\def\mySqrt{\radical"0270373\relax}
\begin{document}
\begin{equation}
w_{n} = \frac{1}{N_d}\mySqrt{\frac{2\epsilon_{s}V_{bi}}{q\left( \dfrac{1}{N_a} + \dfrac{1}{N_d}\right)}}
\end{equation}
\end{document}
Edit: 2021/11/27
Why CM font give us a ugly, sometimes, root (not slanted) instead of other fonts? What is the reason?



\left( ..\right)goes straight at a certain size – David Carlisle Nov 26 '21 at 22:28\dfracterms with inline-fraction equivalents, e.g., by replacing\left( \dfrac{1}{N_a} + \dfrac{1}{N_d}\right)with(1/N_a + 1/N_d). :-) – Mico Nov 26 '21 at 22:31\sqrtor\mySqrtin order to reduce the overall height. – Mico Nov 26 '21 at 22:41