Tunnel Diode

A diode that uses the tunnel effect. It is also called the Esaki diode after its inventor, Leona Esaki. The thickness of the barrier at a pn junction becomes thinner as the impurity density at the junction increases. Consider a junction in which the impurity concentration at both the p and n regions is increased to the point of degeneration, and when a small voltage is applied in the forward direction, as shown in Figure (a), the electrons in the conduction band of the n region tunnel to the vacant level in the valence band of the p region because the junction is very thin, and a current flows. However, as the applied voltage is increased, there are no more vacant levels to which the electrons can transition, so the tunnel current cannot flow and the current actually decreases, and if the voltage is further increased, a forward current of a normal pn junction flows. When a voltage is applied in the reverse direction, the electrons in the valence band of the p region tunnel to the vacant level in the conduction band of the n region due to the tunnel effect. From the above, the current-voltage characteristic of a tunnel diode is as shown in Figure (b). Since there is no time delay in the tunnel current, this element is used for high-speed switches and microwave oscillations. In addition, since the peak value of the tunnel current changes with hydrostatic pressure, it can also be used as a pressure-sensitive element.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

トンネル効果を利用したダイオード．発明者の江崎玲於奈の名をとってエサキダイオードともいう．p-n接合における障壁の厚さは，接合部の不純物密度が大きくなるほど薄くなる．p領域，n領域ともに縮退するまで不純物濃度を大きくした接合で，順方向にわずかに電圧を加えた場合を考えると，図(a)のように，n領域の伝導帯の電子は接合の厚さが非常に薄いので，p領域の価電子帯内の空の準位にトンネル効果によって遷移して電流が流れる．しかし，印加電圧を増していくと，電子にとって遷移できる空の準位がなくなってしまうため，トンネル電流は流れることができず電流はかえって減少し，さらに電圧を増すと普通のp-n接合の順方向電流が流れる．逆方向に電圧を加えたときは，p領域の価電子帯の電子が，n領域の伝導帯の空の準位にトンネル効果によって遷移する．以上のことからトンネルダイオードの電流-電圧特性は図(b)のようになる．トンネル電流は時間的遅れがないので，この素子は高速度スイッチやマイクロ波発振に使われる．また，トンネル電流のピーク値は静水圧によって変化するので，感圧素子としても使える．

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