Microbolometer semiconductor material
View Patent ↗A sensor for detecting intensity of radiation such as of infrared radiation includes an ROIC substrate ( 9 ) and a resistance element ( 1 ) arranged at a distance of the surface of the ROIC substrate. The resistance element comprises one more semiconducting layers such as a silicon semiconducting layer and a semiconducting layer of a silicon-germanium alloy forming a heterojunction. The semiconducting layer or layers can be doped with one or more impurity dopants, the doping level or levels selected so that the layer retains the basic crystallographic properties of the respective material such as those of monosilicon or a monocrystalline silicon-germanium alloy. The impurity dopants are selected from the elements in groups IE, IV, and V, in particular among boron, aluminium, indium, arsenic, phosphorous, antimony, germanium, carbon and tin. The doping can be abrupt so that there is an interior layer inside said semiconducting layer or layers having a significantly higher doping level.
1. A sensor for detecting intensity of radiation, in particular of infrared radiation, including a read-out electronic circuitry (ROIC) substrate and a resistance element arranged at a distance of the surface of the ROIC substrate, wherein the resistance element comprises at least one silicon semiconducting layer and at least one semiconducting layer of a silicon-germanium alloy, a heterojunction being formed between the silicon semiconducting layer and the semiconducting layer of a silicon-germanium alloy.
2. The sensor according to claim 1 , wherein the concentration of the components of the silicon-germanium alloy layer are graded in the thickness direction of the layer.
3. The sensor according to claim 2 , wherein the concentration of Ge in the silicon-germanium alloy layer is graded from a predetermined value to zero over a range smaller than or equal to the thickness of the layer, the predetermined value in particular being equal to 40%.
4. The sensor according to claim 1 , wherein the semiconductors layers of the resistance element form a structure that carries a mirror layer for reflecting the radiation, the mirror layer facing a cavity formed between the resistance element and the ROIC substrate.
5. The sensor according to claim 1 , wherein the atomic concentration of Ge in a semiconducting layer of a silicon-germanium alloy, if such a layer is provided in the resistance element, is less than 40%.
6. The sensor according to claim 1 , wherein at least one of the semiconducting layers, in particular a silicon-germanium alloy layer, comprise carbon, in particular in a concentration less than or equal to 1% (atomic).
7. The sensor according to claim 1 , wherein a silicon semiconducting layer and/or a silicon-germanium alloy layer has an atomically abrupt dopant profile with about 10 to a few 100 nm layer thicknesses and a transition of several orders of o magnitude in concentration over a few nm, in particular 1·10 15 cm −3 to 1·10 19 cm −3 over 10 nm.
8. The sensor according to claim 1 , wherein a silicon semiconducting layer and/or a silicon-germanium alloy layer comprises at least one interior layer region having a doping level that is significantly higher than that of the rest of the layer, the interior layer region in particular having a thickness in the range of 10-1000 nm and in particular a doping level in the range of a 1·10 3 cm 5 times the doping level in the rest of the layer and hi particular also a doping level above the limit for bandgap narrowing typically 1·10 17 cm −3 to 1·10 20 cm −3 .
9. The sensor according to claim 1 , wherein the semiconducting layer or layers is/are composed to make the resistance element have a bias dependent TCR.
10. The sensor according to claim 9 , wherein the resistance element comprises a silicon-germanium layer embedded in between two silicon layers having significantly different thicknesses, the thicknesses in particular differing from one another by more than 10%.
11. The sensor according to claim 1 , wherein the semiconducting layer or layers is/are composed to make the resistance element have a TCR of a zero value, at least at a predetermined temperature.