Chapter 1 – Semiconductor Devices – Part 2 p-n junction diode theory (PN 접합 다이오드 이론) Equilibrium condition (평형 조건) Reverse Bias Current (역 전압 전류) Forward Bias Current (순방향 전압 전류)

Equilibrium Condition (평형 조건/경우) No external voltage is applied ( i.e V = 0).

When the junction is formed, electrons (전자) from the n-side and holes from the p-side will diffuse (확산) leaving behind charged dopant atoms (or dopant ions 도펀트 이온). Remember that the dopant atoms cannot move (움직이지 않는)! Electrons will leave behind +vely charged donor (기증자) atoms and holes will leave behind –vely charged acceptor atoms. A double layer (더블 레이어) of charges (전하들) is formed near the junction (접합의 근처) (space charge region 공간 전하 지역).

5. Space-charge region contains no mobile charge carriers (contains no net charge or the region is neutral), called the depletion region. 6. The net result is the build up of an electric field (전기장). This field gives rise to built-in-potential (내장 잠재력) across the junction. 7. At equilibrium condition (or steady state condition), the net electric field prevents further diffusion (전기장이 추가 확산을 방지한다) of electrons and holes.

Conduction band (전도대) P-type (empty) n-측면 (편) P-측면(편)

Equilibrium Current (평형 전류) Under equilibrium condition, no net current (순 전류 없음) is flowing through the p-n junction diode. Electrons: Electrons in the n-region diffuse into the p-region, giving rise to current, I1. This is compensated by an equal flow of electrons in the reverse direction (drift), giving rise to current I2. So the net electron current at junction is zero. Holes: With the same logic, the net hole current is zero.

2. Biased Condition Electron barrier Hole barrier

Electron Current Reverse Bias: The number of electrons diffusing from the n-region into the p-region is much reduced. ( I1 is reduced). The number of electrons moving from the p-region to the n-region is not affected. (I2 is unchanged). A net current exists. It is limited by the small number of electrons in the p-region.

Forward Bias: The internal barrier is reduced, ( V0 – V), where V is the applied voltage and V0 is the built-in voltage. I1 is large (i.e electron diffusion current). I2 is unaffected ( i.e. electron drift current). The electron current from the n-region to the p-region is controlled by the V (external applied voltage).

the diode leakage current