Semiconductor device MESFET with upper and lower layers

Claim 2

A semiconductor device including a MESFET which has an active layer doped in a GaAs crystal and a threshold voltage V th , the active layer comprising an upper layer having a carrier concentration N 1D and an effective thickness t a1 , and a lower layer having a carrier concentration N 2D and an effective thickness t a2 (N 1D <N 2D ); and which normally operates when a change ΔV th in the threshold voltage V th is within a tolerable amount ΔV thL , an effective thickness t a =t a1 +t a2 of the active layer being t.sub.a <{(2ε·ΔV.sub.thL)/(q·ΔN.sub.D)}.sup.1/2 where ΔN D represents a decrease in the carrier concentrations N 1D , N 2D due to radiation exposure of a total exposure dose R equal to or higher than 1×10 9 roentgens, ε represents a dielectric constant of the active layer, and q represents an electron charge.

Claim 3

A semiconductor device according to claim 1, wherein the decrease ΔN D in the carrier concentrations N 1D , N 2D is given by ΔN.sub.D =b·R.sup.c where b and c are constants.

Claim 4

A semiconductor device according to claim 2, wherein the constants b and c are 1.99×10.sup.10 ≦b≦3.98×10.sup.10 0.5≦c≦0.8.

Claim 5

A semiconductor device including a MESFET which has an active layer doped in a GaAs crystal, the active layer comprising an upper layer having a carrier concentration N 1D , and a lower layer having a carrier concentration N 2D (N 1D <N 2D ); and which normally operates when a change rate α=I dssA /I dss of a saturated drain current I dss of the MESFET, where I dssA represents the value to which the saturated drain current I dss has changed, is within a tolerable rate α L , the carrier concentration N 2D of the lower layer before radiation exposure is given by N.sub.2D >ΔN.sub.D /{1-[α.sub.L (μ/μ.sub.A)].sup.1/2 } where ΔN D represents a decrease in the carrier concentrations N 1D , N 2D of the active layer due to radiation exposure of a total exposure dose R equal to or higher than 1×10 9 roentgens, and μ and μ A represent carrier mobilities in the active layer respectively before and after the radiation exposure.

Claim 6

A semiconductor device including a MESFET which has an active layer doped in a GaAs crystal, the active layer comprising an upper layer having a carrier concentration N 1D , and a lower layer having a carrier concentration N 2D (N 1D <N 2D ); and which normally operates when a change rate α=I dssA /I dss of a saturated drain current I dss of the MESFET, where I dssA represents the value to which the saturated drain current I dss has changed, is within a tolerable rate α L , the carrier concentration N 2D of the lower layer before radiation exposure is given by N.sub.2D >ΔN.sub.D /{1-[α.sub.L (μ/μ.sub.A)].sup.1/2 } where ΔN D represents a decrease in the carrier concentrations N 1D , N 2D of the active layer due to radiation exposure of a total exposure dose R equal to or higher than 1×10 9 roentgens, and μ and μ A represent carrier mobilities in the active layer respectively before and after the radiation exposure.

Claim 7

A semiconductor device according to claim 4, wherein a decrease ΔN D in the carrier concentration is given by ΔN.sub.D =b·R.sup.c where b and c are constants.

Claim 8

A semiconductor device according to claim 5, wherein the constants b and c are 1.99×10.sup.10 ≦b≦3.98×10.sup.10 0.5≦c≦0.8.

Claim 9

A semiconductor device including a MESFET which has an active layer doped in a GaAs crystal, the active layer comprising an upper layer having a carrier concentration N 1D , and a lower layer having a carrier concentration N2 D (N 1D <N 2D ); and which normally operates when a change rate β=g mA /g m of a transconductance g m in the saturation region of the MESFET where g mA represents the value to which the transconductance g m has changed, is within a tolerable rate β L , a carrier concentration N 2D of the lower layer of the active layer before radiation exposure is given by N.sub.2D >ΔN.sub.D /{1-β.sub.L (μ/μ.sub.A)} where ΔN 2D represents a decrease in the carrier concentrations N 1D , N 2D of the active layer due to radiation exposure of a total exposure dose R equal to or higher than 1×10 9 roentgens, and μ and μ A represent carrier mobilities in the active layer respectively before and after the radiation exposure.

Claim 10

A semiconductor device including a MESFET which has an active layer doped in a GaAs crystal, the active layer comprising an upper layer having a carrier concentration N 1D , and a lower layer having a carrier concentration N2 D (N 1D <N 2D ); and which normally operates when a change rate β=g mA /g m of a transconductance g m in the saturation region of the MESFET where g mA represents the value to which the transconductance g m has changed, is within a tolerable rate β L , a carrier concentration N 2D of the lower layer of the active layer before radiation exposure is given by N.sub.2D >ΔN.sub.D /{1-β.sub.L (μ/μ.sub.A)} where ΔN 2D represents a decrease in the carrier concentrations N 1D , N 2D of the active layer due to radiation exposure of a total exposure dose R equal to or higher than 1×10 9 roentgens, and μ and μ A represent carrier mobilities in the active layer respectively before and after the radiation exposure.

Claim 11

A semiconductor device according to claim 7, wherein a decrease ΔN D in the carrier concentration is given by ΔN.sub.D =b·R.sub.c where b and c are constants.

Claim 12

A semiconductor device according to claim 8, wherein the constants b and c are 1.99×10.sup.10 ≦b≦3.98×10.sup.10 0.5≦c≦0.8.

Claim 13

A semiconductor device including a MESFET which has an active layer doped in a GaAs crystal and a threshold voltage V th , the active layer comprising an upper layer having a carrier concentration N 1D and an effective thickness t a1 , and a lower layer having a carrier concentration N 2D and an effective thickness t a2 (N 1D <N 2D ); and which normally operates when a change ΔV th in the threshold voltage V th is within a tolerable amount ΔV thL , and a change rate α=I dssA /I dss of a saturated drain current I dss of the MESFET where I dssA represents the value to which the saturated drain current I dss has changed, is within a tolerable rate α L , where ΔN D represents a decrease in the carrier concentrations N 1D , N 2D of the active layer due to radiation exposure of a total exposure dose R equal to or higher than 1×10 9 roentgens, μ and μ A represent carrier mobilities in the active layer respectively before and after the radiation exposure, ε represents a dielectric constant of the active layer, and q represents an electron charge, an effective thickness t a =t a1 +t a2 of the active layer being t.sub.a <{(2ε·ΔV.sub.thL)/(q·ΔN.sub.D)}1/2 and, a carrier concentration N 2D of the lower layer of the active layer before the radiation exposure is given by N.sub.2D >N.sub.D /{1-[α.sub.L (μ/μ.sub.A)]1/2}.

Claim 14

A semiconductor device including a MESFET which has an active layer doped in a GaAs crystal and a threshold voltage V th , the active layer comprising an upper layer having a carrier concentration N 1D and an effective thickness t a1 , and a lower layer having a carrier concentration N 2D and an effective thickness t a2 (N 1D <N 2D ); and which normally operates when a change ΔV th in the threshold voltage V th is within a tolerable amount ΔV thL , and a change rate α=I dssA /I dss of a saturated drain current I dss of the MESFET where I dssA represents the value to which the saturated drain current I dss has changed, is within a tolerable rate α L , where ΔN D represents a decrease in the carrier concentrations N 1D , N 2D of the active layer due to radiation exposure of a total exposure dose R equal to or higher than 1×10 9 roentgens, μ and μ A represent carrier mobilities in the active layer respectively before and after the radiation exposure, ε represents a dielectric constant of the active layer, and q represents an electron charge, an effective thickness t a =t a1 +t a2 of the active layer being t.sub.a <{(2ε·ΔV.sub.thL)/(q·ΔN.sub.D)}1/2 and, a carrier concentration N 2D of the lower layer of the active layer before the radiation exposure is given by N.sub.2D >N.sub.D /{1-[α.sub.L (μ/μ.sub.A)]1/2}.

Claim 15

A semiconductor device according to claim 10, wherein a decrease ΔN D in the carrier concentration is given by N.sub.D =b·R.sup.c where b and c are constants.

Claim 16

A semiconductor device according to claim 11, wherein the constants b and c are 1.99×10.sup.10 ≦b≦3.98×10.sup.10 0.5≦c≦0.8.

Claim 17

A semiconductor device including a MESFET which has an active layer doped in a GaAs crystal and a threshold voltage V th , the active layer comprising an upper layer having a carrier concentration N 1D and an effective thickness t a1 , and a lower layer having a carrier concentration N 2D and an effective thickness t a2 (N 1D <N 2D ); and which normally operates when a change ΔV th in the threshold voltage V th is within a tolerable amount ΔV thL , and a change rate β=g mA /g m of a transconductance g m in the saturation region of the MESFET where g mA represents a transconductance to which the transconductance g m has changed, is within a tolerable rate β L , where a decrease ΔN D in the carrier concentration N 1D , N 2D due to radiation exposure of a total exposure dose R equal to or higher than 1×10 9 roentgens, μ and μ A represent carrier mobilities in the active layer respectively before and after the radiation exposure, ε represents a dielectric constant of the active layer, and q represents an electron charge, an effective thickness t a =t a1 +t a2 of the active layer being t.sub.a <{(2ε·ΔV.sub.thL)/(q·ΔN.sub.d)}1/2, and a carrier concentration N 2D of the lower layer of the active layer before the radiation exposure being N.sub.2D >ΔN.sub.D /{1-β.sub.L (μ/μ.sub.A)}.

Claim 18

A semiconductor device including a MESFET which has an active layer doped in a GaAs crystal and a threshold voltage V th , the active layer comprising an upper layer having a carrier concentration N 1D and an effective thickness t a1 , and a lower layer having a carrier concentration N 2D and an effective thickness t a2 (N 1D <N 2D ); and which normally operates when a change ΔV th in the threshold voltage V th is within a tolerable amount ΔV thL , and a change rate β=g mA /g m of a transconductance g m in the saturation region of the MESFET where g mA represents a transconductance to which the transconductance g m has changed, is within a tolerable rate β L , where a decrease ΔN D in the carrier concentration N 1D , N 2D due to radiation exposure of a total exposure dose R equal to or higher than 1×10 9 roentgens, μ and μ A represent carrier mobilities in the active layer respectively before and after the radiation exposure, ε represents a dielectric constant of the active layer, and q represents an electron charge, an effective thickness t a =t a1 +t a2 of the active layer being t.sub.a <{(2ε·ΔV.sub.thL)/(q·ΔN.sub.d)}1/2, and a carrier concentration N 2D of the lower layer of the active layer before the radiation exposure being N.sub.2D >ΔN.sub.D /{1-β.sub.L (μ/μ.sub.A)}.

Claim 19

A semiconductor device according to claim 13, wherein a decrease ΔN D in the carrier concentration is given by ΔN.sub.D =b·R.sup.c where b and c are constants.

Claim 20

A semiconductor device according to claim 14, wherein the constants b and c are 1.99×10.sup.10 ≦b≦3.98×10.sup.10 0.5≦c≦0.8.

Claim 21

A semiconductor device including a MESFET having an active layer doped in a GaAs crystal, the active layer comprising an upper layer having a carrier concentration N 1D , and a lower layer having a carrier concentration N 2D (N 1D <N 2D ); and which normally operates when a change rate α=I dssA /I dss of a saturated drain current I dss of the MESFET where I dssA represents the value to which the saturated drain current I dss has changed, is within a tolerable rate α L , and a change rate β=g mA /g m of a transconductance in the saturation region of the MESFET where g mA represents the value to which the transconductance g m has changed, is within a tolerable rate β L , a carrier concentration N 2D of the lower layer of the active layer before radiation exposure being N.sub.2D >ΔN.sub.D /{1-[α.sub.L (μ/μ.sub.A)].sup.178 }, and N.sub.2D >ΔN.sub.D /{1-β.sub.L (μ/μ.sub.A)} where ΔN D represents a decrease in the carrier concentrations N 1D , N 2D of the active layer due to radiation exposure of a total exposure dose R equal to or higher than 1×10 9 roentgens, and μ and μ A represent carrier mobilities in the active layer respectively before and after the radiation exposure.

Claim 22

A semiconductor device including a MESFET having an active layer doped in a GaAs crystal, the active layer comprising an upper layer having a carrier concentration N 1D , and a lower layer having a carrier concentration N 2D (N 1D <N 2D ); and which normally operates when a change rate α=I dssA /I dss of a saturated drain current I dss of the MESFET where I dssA represents the value to which the saturated drain current I dss has changed, is within a tolerable rate α L , and a change rate β=g mA /g m of a transconductance in the saturation region of the MESFET where g mA represents the value to which the transconductance g m has changed, is within a tolerable rate β L , a carrier concentration N 2D of the lower layer of the active layer before radiation exposure being N.sub.2D >ΔN.sub.D /{1-[α.sub.L (μ/μ.sub.A)].sup.178 }, and N.sub.2D >ΔN.sub.D /{1-β.sub.L (μ/μ.sub.A)} where ΔN D represents a decrease in the carrier concentrations N 1D , N 2D of the active layer due to radiation exposure of a total exposure dose R equal to or higher than 1×10 9 roentgens, and μ and μ A represent carrier mobilities in the active layer respectively before and after the radiation exposure.

Claim 23

A semiconductor device according to claim 16, wherein a decrease ΔN D in the carrier concentration is given by ΔN.sub.D =b·R.sup.c where b and c are constants.

Claim 24

A semiconductor device according to claim 17, wherein the constants b and c are 1.99×10.sup.10 ≦b≦3.98×10.sup.10 0.5≦c≦0.8.

Claim 25

A semiconductor device including a MESFET having an active layer doped in a GaAs crystal and a threshold voltage V th , the active layer comprising an upper layer having a carrier concentration N 1D and an effective thickness t a1 , and a lower layer having a carrier concentration N 2D and an effective thickness t a2 (N 1D <N 2D ); and which normally operates when a change ΔV th in the threshold voltage V th is within a tolerable amount ΔV thL , a change rate α=I dssA /I dss of a saturated drain current I dss of the MESFET where I dssA represents the value to which the saturated drain current I dss has changed, is within a tolerable rate α L , and a change rate β=g mA /g m of a transconductance g m in the saturation region of the MESFET where g mA represents the value to which the transconductance g m has changed, is within a tolerable rate β L , where ΔN D represents a decrease in the carrier concentrations N 1D , N 2D due to radiation exposure of a total exposure dose R equal to or higher than 1×10 9 roentgens, μ and μ A represent carrier mobilities in the active layer respectively before and after radiation exposure, ε represents a dielectric constant of the active layer, and q represents an electron charge, an effective thickness t a =t a1 +t a2 of the active layer being t.sub.a <{(2ε·αV.sub.thL)/(q·ΔN.sub.D)}.sup.1/2, and a carrier concentration N 2D of the lower layer of the active layer before the radiation exposure being N.sub.2D >ΔN.sub.D /{1-[α.sub.L (μ/μ.sub.A)].sup.1/2 } and N.sub.2D >ΔN.sub.D /{1-β.sub.L (μ/μ.sub.A)}.

Claim 26

A semiconductor device including a MESFET having an active layer doped in a GaAs crystal and a threshold voltage V th , the active layer comprising an upper layer having a carrier concentration N 1D and an effective thickness t a1 , and a lower layer having a carrier concentration N 2D and an effective thickness t a2 (N 1D <N 2D ); and which normally operates when a change ΔV th in the threshold voltage V th is within a tolerable amount ΔV thL , a change rate α=I dssA /I dss of a saturated drain current I dss of the MESFET where I dssA represents the value to which the saturated drain current I dss has changed, is within a tolerable rate α L , and a change rate β=g mA /g m of a transconductance g m in the saturation region of the MESFET where g mA represents the value to which the transconductance g m has changed, is within a tolerable rate β L , where ΔN D represents a decrease in the carrier concentrations N 1D , N 2D due to radiation exposure of a total exposure dose R equal to or higher than 1×10 9 roentgens, μ and μ A represent carrier mobilities in the active layer respectively before and after radiation exposure, ε represents a dielectric constant of the active layer, and q represents an electron charge, an effective thickness t a =t a1 +t a2 of the active layer being t.sub.a <{(2ε·αV.sub.thL)/(q·ΔN.sub.D)}.sup.1/2, and a carrier concentration N 2D of the lower layer of the active layer before the radiation exposure being N.sub.2D >ΔN.sub.D /{1-[α.sub.L (μ/μ.sub.A)].sup.1/2 } and N.sub.2D >ΔN.sub.D /{1-β.sub.L (μ/μ.sub.A)}.

Claim 27

A semiconductor device according to claim 19, wherein a decrease ΔN D in the carrier concentration is given by ΔN.sub.D =b·R.sup.c where b and c are constants.

Claim 28

A semiconductor device according to claim 20, wherein the constants b and c are 1.99×10.sup.10 ≦b ≦3.98×10.sup.10 0.5≦c≦0.8.

Claim 29

A semiconductor device according to claim 2, wherein the constants b and c are 5×10.sup.5 ≦b≦1×10.sup.6 1.0≦c≦1.3.

Claim 30

A semiconductor device according to claim 5, wherein the constants b and c are 5×10.sup.5 ≦b≦1×10.sup.6 1.0≦c≦1.3.

Claim 31

A semiconductor device according to claim 8, wherein the constants b and c are 5×10.sup.5 ≦b≦1×10.sup.6 1.0≦c≦1.3.

Claim 32

A semiconductor device according to claim 11, wherein the constants b and c are 5×10.sup.5 ≦b≦1×10.sup.6 1.0≦c≦1.3.

Claim 33

A semiconductor device according to claim 14, wherein the constants b and c are 5×10.sup.5 ≦b≦1×10.sup.6 1.0≦c≦1.3.

Claim 34

A semiconductor device according to claim 17, wherein the constants b and c are 5×10.sup.5 ≦b≦1×10.sup.6 1.0≦c≦1.3.

Claim 35

A semiconductor device according to claim 20, wherein the constants b and c are 5×10.sup.5 ≦b≦1×10.sup.6 1.0≦c≦1.3.