Semiconductor device
A layer in which the potential level difference normally unrequired for device operation is generated is positively inserted in a device structure. The potential level difference has such a function that even if a semiconductor having a small bandgap is exposed on a mesa side surface, a potential drop amount of the portion is suppressed, and a leakage current inconvenient for device operation can be reduced. This effect can be commonly obtained for a heterostructure bipolar transistor, a photodiode, an electroabsorption modulator, and so on. In the photodiode, since the leakage current is alleviated, the device size can be reduced, so that in addition to improvement of operating speed with a reduction in series resistance, it is advantageous that the device can be densely disposed in an array.
1. A semiconductor device comprising a laminate structure comprising a first semiconductor layer provided on one side of a substrate in parallel with a surface of the substrate surface, a p-type second semiconductor layer, an n-type third semiconductor layer, and at least one of an n-type fourth semiconductor layer and a p-type fifth semiconductor layer, wherein
the first semiconductor layer is disposed between the second semiconductor layer and the third semiconductor layer and has an impurity concentration lower than the impurity concentrations of the second and third semiconductor layers,
the fourth semiconductor layer is disposed between the first semiconductor layer and the second semiconductor layer and has a bandgap larger than that of the first semiconductor layer,
the fifth semiconductor layer is disposed between the first semiconductor layer and the third semiconductor layer and has a bandgap larger than that of the first semiconductor layer, when the second semiconductor layer is far from the substrate relative to the third semiconductor layer, the fourth semiconductor layer is essential, the outer circumference of the second semiconductor layer is more inward than the outer circumference of the fourth semiconductor layer,
when the third semiconductor layer is far from the substrate relative to the second semiconductor layer, the fifth semiconductor layer is essential, and the outer circumference of the third semiconductor layer is more inward than the outer circumference of the fifth semiconductor layer.
2. The semiconductor device according to claim 1 , wherein in a case where the second semiconductor layer is far from the substrate relative to the third semiconductor layer,
when a reverse bias is applied to between the second semiconductor layer and the fourth semiconductor layer, a potential difference of not less than 0.2 V and not more than 1.0 V is generated in the fourth semiconductor layer.
3. The semiconductor device according to claim 2 , further comprising an n-type sixth semiconductor layer adjacent to the opposite side of the fourth semiconductor layer of the second semiconductor layer when the second semiconductor layer is far from the substrate relative to the third semiconductor layer.
4. The semiconductor device according to claim 1 , wherein in a case where the third semiconductor layer is far from the substrate relative to the second semiconductor layer, when a reverse bias is applied to between the third semiconductor layer and the fifth semiconductor layer, a potential difference of not less than 0.2 V and not more than 1.0 V is generated in the fifth semiconductor layer.
5. The semiconductor device according to claim 4 , further comprising a p-type seventh semiconductor layer adjacent to the opposite side of the fifth semiconductor layer of the third semiconductor layer when the third semiconductor layer is far from the substrate relative to the second semiconductor layer.
6. The semiconductor device according to claim 1 , further comprising an n-type sixth semiconductor layer adjacent to the opposite side of the fourth semiconductor layer of the second semiconductor layer when the second semiconductor layer is far from the substrate relative to the third semiconductor layer.
7. The semiconductor device according to claim 1 further comprising a p-type seventh semiconductor layer adjacent to the opposite side of the fifth semiconductor layer of the third semiconductor layer when the third semiconductor layer is far from the substrate relative to the second semiconductor layer.