Heterostructure for a high electron mobility transistor and a method of producing the same
The present document discloses a heterostructure for a high electron mobility transistor (HEMT). The heterostructure comprises a SiC substrate, an In x Al y Ga 1-x-y N nucleation layer ( 12 ), wherein x=0-1, y=0-1, preferably x<0.05 and y>0.50, more preferably x<0.03 and y>0.70 and most preferably x<0.01 and y>0.90, formed on the SiC substrate. The heterostructure further comprises a GaN channel layer formed on the In x Al y Ga 1-x-y N nucleation layer. A thickness of the GaN channel layer is 50 to 500 nm, preferably 100 to 450 nm, most preferably 150 to 400 nm. The GaN channel layer presents a rocking curve with a (002) peak having a FMHW below 300 arcsec, and a rocking curve with a (102) peak having a FMHW below 400 arcsec as determined by X-ray diffraction, XRD. A surface of an uppermost layer of the heterostructure ( 1 ) exhibits an atomic step-flow morphology with rms roughness over a 10 μm 2 scan area of below 1.8 nm, preferably below 1.4 nm, most preferably below 1 nm, over a 3 μm 2 scan area of below 1 nm, preferably below 0.7 nm, most preferably below 0.4 nm, as determined by atomic force microscopy, AFM.
1. A heterostructure for a high electron mobility transistor (HEMT), comprising:
a SiC substrate,
an In x Al y Ga 1-x-y N nucleation layer, wherein x=0-1, y=0-1, formed directly on the SiC substrate, and
a GaN channel layer formed directly on the In x Al y Ga 1-x-y N nucleation layer, and
a barrier layer formed on the GaN channel layer,
wherein:
a thickness of the GaN channel layer is 50 to 500 nm;
a total thickness of the heterostructure, consisting of the In x Al y Ga 1-x-y N nucleation layer, the GaN channel layer, and the barrier layer, not including a thickness of the SiC substrate, is in a range of 54 nm to 730 nm;
the In x Al y Ga 1-x-y N nucleation layer is fully strained, wherein its in-plane lattice constant is exactly the same as an in-plane lattice constant of the SiC substrate, or is within +/−0.15% of an in-plane lattice constant of the SiC substrate;
the GaN channel layer presents a rocking curve with a (002) peak having a full width half maximum (FWHM) below 300 arcsec, and a rocking curve with a (102) peak having a FWHM below 400 arcsec as determined by X-ray diffraction (XRD); and
a surface of the GaN channel layer of the heterostructure prior to formation of any additional layers thereon exhibits root mean square (RMS) roughness of below 1.8 nm over a 10×10 μm 2 scan area, or of below 1 nm over a 3×3 μm 2 scan area.
2. The heterostructure according to claim 1 , wherein the In x Al y Ga 1-x-y N nucleation layer has a homogenous or varying content of Al.
3. The heterostructure according to claim 1 , further comprising an AlN exclusion layer formed on the GaN channel layer, and the barrier layer formed on the AlN exclusion layer.
4. The heterostructure according to claim 3 , further comprising a passivation layer of SiN or GaN formed on the barrier layer.
5. The heterostructure according to claim 1 , wherein an unintentional doping concentration of carbon in the GaN channel layer is less than 1E+17 cm −2 .
6. A method of producing a heterostructure according to claim 1 , by metal organic chemical vapor deposition (MOCVD), for a high electron mobility transistor (HEMT), the method comprising:
providing a SiC substrate,
providing an In x Al y Ga 1-x-y N nucleation layer, wherein x=0-1, y=0-1, formed directly on the SiC substrate,
providing a GaN channel layer formed directly on the In x Al y Ga 1-x-y N nucleation layer, and
providing a barrier layer formed on the GaN channel layer,
wherein the pressure upon growth of the In x Al y Ga 1-x-y N nucleation layer and of the GaN channel layer is 20 to 200 mbar,
the temperature upon growth of the In x Al y Ga 1-x-y N nucleation layer is 900 to 1200° C., and
the temperature upon growth of the GaN channel layer is 1000 to 1150° C.
7. The method of producing a heterostructure for a high electron mobility transistor (HEMT) according to claim 6 , comprising a further step of providing an AlGaN exclusion layer, wherein the Al content is 40 to 80%, between the barrier layer and the GaN channel layer.
8. The method of producing a heterostructure for a high electron mobility transistor (HEMT) according to claim 6 , comprising a further step of providing a passivation layer of SiN or GaN on the barrier layer.
9. A method of producing a HEMT device, comprising the steps of providing a heterostructure according to claim 8 , and providing a source, a gate contact and a drain contact onto the passivation layer.
10. The method according to claim 9 , further comprising the step of providing an insulating layer between the passivation layer and the gate contact.
11. A method of producing a heterostructure according to claim 1 , by metal organic chemical vapor deposition (MOCVD), for a high electron mobility transistor (HEMT), the method comprising the steps of:
providing a SiC substrate;
growing an In x Al y Ga 1-x-y N nucleation layer, wherein x=0-1, y=0-1, directly on the SiC substrate;
growing a GaN channel layer directly on the In x Al y Ga 1-x-y N nucleation layer; and
growing a barrier layer on the GaN channel layer.
12. The method of claim 11 , wherein the In x Al y Ga 1-x-y N nucleation layer has a homogenous or varying content of Al.
13. The method of claim 11 , further comprising forming an AlN exclusion layer on the GaN channel layer, and forming the barrier layer on the AlN exclusion layer.
14. The method of claim 13 , further comprising forming a passivation layer of SiN or GaN on the barrier layer.