Why hole diffusion current is negative?

The concentration of holes is decreasing as you go from the -x to +x direction. Therefore, holes will diffuse to the +x direction where there’s a lower concentration of holes. This is why the negative sign is needed in the equation for the hole diffusion current.

Why is current density negative?

Current is calculated as the scalar product of the current vector and the surface normal. If they are in opposite directions, current density is negative.

Can electron current density be negative?

As soon as it is declared that the direction of the current density shall be called positive when the positive particles move (and the negative particles don’t move) then it must follow that when the negative particles move (and the positive particles don’t move), the direction of the current density must be called …

Why electron diffusion current is positive?

The change of concentration is described by a gradient which points in the direction of the higher (!) concentration. In other words they move in the direction of the negative gradient. This is where the additional minus sign comes in so that the current becomes positive.

Why electron diffusion current is positive and hole diffusion current is negative?

Holes have +ve charge while electrons possess negative charge. But dp/dx and dn/dx are both negative that’s why hole current density is negative and electron current density is positive.

What is the electron diffusion current density?

Diffusion current Density is a current in a semiconductor caused by the diffusion of charge carriers (holes and/or electrons). This is the current which is due to the transport of charges occurring because of non-uniform concentration of charged particles in a semiconductor.

Is current density always positive?

I know that current density always points in the direction of flow of positive charge.

Is current density positive?

The current density vector is defined as a vector whose magnitude is the electric current per cross-sectional area at a given point in space, its direction being that of the motion of the positive charges at this point….

What is hole diffusion?

How do you find electron diffusion current density?

The diffusion current density can be calculated by equation 1. 1. Where e− = −1.602·10−19C is the elemental charge. Dp,n are the diffusion constants for hole and electrons, respectivly.

What is the hole diffusion constant?

The diffusion constant for electrons is Dn = 22.5cm2/s, the diffusion constant for holes is Dp = 5.2cm2/s, and the temperature is 300 K. p and n are the hole and electron concentrations.

What is diffusion current and diffusion current density?

The diffusion current density is directly proportional to the concentration gradient. Concentration gradient is the difference in concentration of electrons or holes in a given area. If the concentration gradient is high, then the diffusion current density is also high.

Why is the current density of a hole negative?

Holes do not exist, they are simply deficits of electrons. Thus, the hole current density seems to counter electron current density. Holes have +ve charge while electrons possess negative charge. But dp/dx and dn/dx are both negative that’s why hole current density is negative and electron current density is positive.

Why is the diffusion current density of injected electrons negative?

Here, you need to understand that the concentration profile of injected electrons and holes (which contribute to the red underlined term, to which you are probably referring to) has a negative slope: So both dn/dx and dp/dx are negative which causes the diffusion current density to be negative for electrons and positive for holes.

What is the difference between electron current and hole current?

The current that flows due to holes is called hole current and the current that flows due to electrons is called electron current. How this 19-year-old earns an extra $3600 per week. His friends were in awe when they saw how much money he was making. In a semiconductor there are holes and electrons.

How does a hole current occur in a semiconductor?

Hole current in a semiconductor happens when the valence band electrons from an adjacent atom shift to complete a hole (broken covalent bond) in the neighbouring atom. The electron which was released from the broken covalent bond moves freely in the semiconductor.