How does the junction width change when a p-n junction is forward biased ?

Explanation

Formation of junction diode. When a p-type crystal is place in contact with n-type crystal so as to form one piece, the assembly so obtained is called p-n junction or junction diode or crystal diode. The surface of contact of p-type and n-type crystals is called junction. In the p-section, holes are the majority carriers while in n-section, the majority carriers are electrons. Due to high concentration of different types of charge carriers in the two sections, holes from p-region diffuse into n-region and electrons from n-region diffuse into p-region. In both cases, when an electron meets a hole they cancel the effect of each other and as a result, a thin layer at the junction becomes devoid of charge carriers. This is called depletion layer as shown in the figure. The thickness of depletion layer is of the order of `10^(-6)m`.
Change in thickness of depletion layer with foward bias. Initially when forward bias voltage is zero, current is also zero. When p-n junction is forward biased, the positive holes in the p-type material are repelled by the positive voltage towards the junction. Simultaneously the free elctrons in the p-type material are replled by the negative voltage towards the junction (a minimum voltage of `0.7V` for `Si` and `0.3V` for `Ge` is needed to overcome the potential barrier at the junction) See fig. Practically no current flows until the barrier is overcome.

As bias voltage is increased, little by little current remains zero till bias voltage is `0.3V` (potential barrier). When bias voltage increases from potential barrier, current starts flowing and the thickness of depletion layer starts decreasing and becomes minimum at potential barrier.