Semiconductor device and method of forming the same

Abstract

A diode, UV radiation detector, and method of manufacturing semiconductor device that includes a diode with a substrate having a first side and a second side. The diode includes an active layer having a rocksalt phase crystalline structure of CaS disposed on the first side of the substrate, and an electrical contact disposed on the second side of the substrate. The diode also includes a semi-transparent conducting layer disposed on the active layer. The UV radiation detector includes the diode and circuitry connecting the semi-transparent conducting layer and the electrical contact. The UV radiation detector may detect radiation having a wavelength between 220 and 280 nm. The substrate may have a lattice mismatch between 0.47% and 12.6% with respect to the active layer.

What is claimed is: 
     
         1 . A diode, the diode comprising:
 a substrate having a first side and a second side, the first side and the second side being located on opposing faces of the substrate;   an active layer comprising rocksalt phase crystalline structure CaS disposed on the first side of the substrate;   an electrical contact disposed on the second side of the substrate; and   a semi-transparent conducting layer disposed on the active layer.   
     
     
         2 . The diode of  claim 1 , wherein the substrate has a lattice constant of 5.69 Å. 
     
     
         3 . The diode of  claim 1 , the diode being a Schottky-barrier diode that is operated in a zero-bias mode. 
     
     
         4 . The diode of  claim 1 , wherein active layer is between 20-50 nm thick. 
     
     
         5 . The diode of  claim 3 , wherein an external quantum efficiency of the Schottky-barrier diode is at least 19% at a wavelength of 235 nm. 
     
     
         6 . The diode of  claim 1 , wherein the substrate is a n + -GaAs substrate. 
     
     
         7 . The Schottky-barrier diode of  claim 1 , wherein the semi-transparent conducting layer is a 10 nm thick layer of gold. 
     
     
         8 . A UV radiation detector comprising:
 a diode, the diode comprising:
 a substrate having a first side and a second side, the first side and the second side being located on opposing faces of the substrate; 
 an active layer comprising rocksalt phase crystalline structure CaS disposed on the first side of the substrate; 
 an electrical contact disposed on the second side of the substrate; and 
 a semi-transparent conducting layer disposed on the active layer; and 
   a circuit connecting the semi-transparent conducting layer and the electrical contact,   wherein the UV radiation detector is configured to detect radiation having a wavelength between 220 and 280 nm.   
     
     
         9 . The UV radiation detector according to  claim 8 , wherein the diode is a Schottky-barrier diode having an external quantum efficiency of at least 19% at a wavelength of 235 nm when operated in zero-bias mode. 
     
     
         10 . A method of manufacturing semiconductor device, the method comprising:
 growing a binary molecular precursor layer on a substrate, the substrate heated to a first temperature, using molecular beam epitaxy on one side of a substrate,   ramping the temperature of the substrate at a first rate to a second temperature while under the flux of the molecular beam epitaxy;   holding the temperature of the substrate at the second temperature for a first period of time while under the flux of the molecular beam epitaxy;   reducing the temperature of the substrate at a second rate to a third temperature while under the flux of the molecular beam epitaxy; and   growing a second layer, the second layer being formed of the same binary molecular material as the precursor layer, on the binary molecular precursor layer for a second period of time to form an active layer including the first layer and second layer,   wherein the substrate has a lattice mismatch between 0.47% and 12.6% with respect to the active layer.   
     
     
         11 . The method of  claim 10 , wherein the binary molecular precursor layer is a CaS layer. 
     
     
         12 . The method of  claim 11 , wherein Ca and S sources in the molecular beam epitaxy are maintained at 430° C. and 910° C. respectively. 
     
     
         13 . The method of  claim 12 , wherein the binary molecular precursor layer is grown to a thickness of 5 nm. 
     
     
         14 . The method according to  claim 13 , wherein the active layer is grown to a thickness of 20 nm. 
     
     
         15 . The method of  claim 10 , further comprising:
 disposing a semi-transparent conducting layer on the active layer;   disposing an electrical contact on a side of substrate opposite to the active layer; and   electrically connecting a circuit to the electrical contact and the semi-transparent conducting layer to a circuit.   
     
     
         16 . The method of  claim 12 , wherein the first temperature is 180° C., the first rate is 50° C./min, the second temperature is 550° C., the first period of time is 30 minutes, the third temperature is 350° C., the second period of time is 30 minutes, and the second rate is −30° C./min. 
     
     
         17 . The method of  claim 10 , wherein the binary molecular precursor layer is a CaTe layer. 
     
     
         18 . The method of  claim 17 ,
 wherein the first temperature is 200° C., the first rate is +50° C./min, the second temperature is 300° C., the first period of time is 30 minutes, the third temperature is 230° C., the second period of time is 30 minutes, and the second rate is −30° C./min, and   wherein a source temperature of an elemental Ca source and a source temperature of an elemental Te source in the molecular beam epitaxy are 485° C. and 290° C., respectively.   
     
     
         19 . The method of  claim 10 , wherein the first and second periods of time are determined by monitoring a crystalline quality of the binary molecular precursor layer and active layer using reflection high energy diffraction (RHEED). 
     
     
         20 . The method of  claim 10 , wherein the active layer is grown to a thickness greater than 20 nm.