the various features and advantages of the present invention can be understood more thoroughly through the following detailed descriptions together with the attached drawings . now , please refer to the attached drawings as we describe the various embodiments of the present invention . fig3 shows a gallium - nitride based light emitting diode structure 30 with enhanced light illuminance according to the first embodiment of the present invention , comprising : substrate 31 , buffer layer 32 , n - type gallium nitride ( gan ) layer 33 , active light - emitting - layer 34 , p - type cladding layer 35 , p - type contact layer 36 , barrier buffer layer 37 , transparent contact layer 38 , and n - type electrode layer 39 . the bottom layer of the structure is substrate 31 , and it is made of sapphire . and next , the buffer layer 32 is formed on substrate 31 , and it is made of aluminum - gallium - indium - nitride ( al 1 - x - y ga x in y n ) wherein 0 ≦ x ≦ 1 , 0 ≦ y ≦ 1 and x + y ≦ 1 . the n - type gallium - nitride ( gan ) layer 33 is formed on buffer layer 32 . the active light - emitting - layer 34 is formed on n - type gallium - nitride ( gan ) layer 33 , and it is made of indium - gallium - nitride ( ingan ). and next , the p - type cladding layer 35 is formed on active light - emitting - layer 34 , and it is made of mg - doped aluminum - indium - nitride ( al 1 - x in x n ), wherein 0 ≦ x & lt ; 1 . then , p - type contact layer 36 is formed on p - type cladding layer 35 , and it is made of gallium nitride ( gan ). and then barrier buffer layer 37 is formed on p - type contact layer 36 , and it is made of magnesium - nitride ( mgn ). and next transparent contact layer 38 is formed on barrier buffer layer 37 , and it is made of indium - tin - oxide . and finally the n - type electrode layer 39 is formed on n - type gallium nitride ( gan ) layer 33 , and it is made of ti / al or cr / au . in the above - mentioned structure , the thickness of the barrier buffer layer ( mgn ) 37 is between 2 å and 200 å , and its growth temperature is between 500 ° c . and 1200 ° c . in the embodiment 1 , we can also use undoped indium nitride ( inn ) or undoped indium gallium nitride ( in x ga 1 - x n ; 0 & lt ; x & lt ; 1 ) instead of magnesium - nitride ( mgn ) as the barrier buffer layer 37 . the thickness of the barrier buffer layer ( inn or in x ga 1 - x n ; 0 & lt ; x & lt ; 1 ) 37 is between 2 å and 200 å , and its growth temperature is between 500 ° c . and 1200 ° c . fig4 shows a gallium - nitride based light emitting diode structure 40 with enhanced light illuminance according to a second embodiment of the present invention , comprising : substrate 41 , buffer layer 42 , n - type gallium - nitride ( gan ) layer 43 , active light - emitting - layer 44 , p - type cladding layer 45 , p - type contact layer 46 , short - period super - lattice barrier buffer layer 47 , transparent contact layer 48 , and n - type electrode layer 49 . the bottom layer of the structure is substrate 41 , and it is made of sapphire . and next , the buffer layer 42 is formed on substrate 41 , and it is made of aluminum - gallium - indium - nitride ( al 1 - x - y ga x in y n ), wherein 0 ≦ x ≦ 1 , 0 ≦ y ≦ 1 and x + y ≦ 1 . then , the n - type gallium - nitride ( gan ) layer 43 is formed on buffer layer 42 . and then , the active light - emitting - layer 44 is formed on n - type gallium nitride ( gan ) layer 43 , and it is made of indium - gallium nitride ( ingan ). and next the p - type cladding layer 45 is formed on active light - emitting - layer 44 , and it is made of mg - doped aluminum - indium - nitride ( al 1 - x in x n ), wherein 0 ≦ x & lt ; 1 . then , p - type contact layer 46 is formed on p - type cladding layer 45 , and it is made of gallium nitride ( gan ). and then , the short - period super - lattice barrier buffer layer 47 is formed on p - type contact layer 46 , and it is made of magnesium - nitride / undoped - indium - nitride ( mgn / inn ). and next the transparent contact layer 48 is formed on the short - period super - lattice barrier buffer layer 47 , and it is made of indium - tin - oxide . and finally the n - type electrode layer 49 is formed on n - type gallium - nitride ( gan ) layer 43 , and it is made of ti / al or cr / au . in the above - mentioned structure , the thickness of the respective portions of the short - period super - lattice barrier buffer layer 47 made of ( mgn / inn ) is between 2 and 200 å respectively , its number of repetition is 2 or above , and its configuration can be mgn up / inn down or mgn down / inn up , and its growth temperature is between 500 ° c . and 1200 ° c . fig5 shows a gallium - nitride based light emitting diode structure 50 with enhanced light illuminance according to a third embodiment of the present invention , comprising : substrate 51 , buffer layer 52 , n - type gallium nitride ( gan ) layer 53 , active light - emitting - layer 54 , p - type cladding layer 55 , p - type contact layer 56 , short - period super - lattice barrier buffer layer 57 , transparent contact layer 58 , and n - type electrode layer 59 . the bottom layer of the structure is substrate 51 , and it is made of sapphire . and next , the buffer layer 52 is formed on substrate 51 , and it is made of aluminum - gallium - indium - nitride ( al 1 - x - y ga x in y n ), wherein 0 ≦ x ≦ 1 , 0 ≦ y ≦ 1 and x + y ≦ 1 . then , the n - type gallium nitride ( gan ) layer 53 is formed on buffer layer 52 . and then , the active light - emitting - layer 54 is formed on n - type gallium nitride ( gan ) layer 53 , and it is made of indium - gallium nitride ( ingan ). and next , the p - type cladding layer 55 is formed on active light - emitting - layer 54 , and it is made of mg - doped aluminum - indium - nitride ( al 1 - x in x n ), wherein 0 ≦ x & lt ; 1 . then , p - type contact layer 56 is formed on p - type cladding layer 55 , and it is made of gallium nitride ( gan ). and then , the short - period super - lattice barrier buffer layer 57 is formed on p - type contact layer 56 , and it is made of magnesium - nitride / undoped - indium - gallium - nitride ( mgn / in x ga 1 - x n ). and next , the transparent contact layer 58 is formed on the short - period super - lattice barrier buffer layer 57 , and it is made of indium - tin - oxide . and finally , the n - type electrode layer 59 is formed on n - type gallium nitride ( gan ) layer 53 , and it is made of ti / al or cr / au . in the above - mentioned structure , the thicknesses of the respective portions of the short - period super - lattice barrier buffer layer 57 made of ( mgn / in x ga 1 - x n ) are between 2 and 200 å respectively , its number of repetition is 2 or above , and its configuration can be mgn up / in x ga 1 - x n down or mgn down / in x ga 1 - x n up , and its growth temperature is between 500 ° c . and 1200 ° c . in the above - mentioned three embodiments , indium - tin - nitride ( ito ) is utilized as the material of the transparent conductive layer . however , the material utilized for the transparent conductive layer of the present invention is not restricted to ito , and it may comprise for example ito , cto , zno : al , znga 2 o 4 , sno 2 : sb , ga 2 o 3 : sn , agino 2 : sn , and in 2 o 3 : zn for the n - type transparent conductive oxide ( tco ) layer , and cualo 2 , lacuos , nio , cugao 2 , srcu 2 o 2 for the p - type transparent conductive oxide ( tco ) layer . from the three embodiments described in detail above , and the related experimental data as shown in fig2 , it is evident that the shortcomings and restrictions of the prior art light emitting diode can certainly be improved by means of the light emitting diode structure of the present invention . and in particular the light transmittance of this kind of light emitting diode can be raised from 62 % of the prior art to 95 % or above of the present invention , and its light illuminance and light transmittance efficiency can also be raised significantly . therefore , the present invention does have its value of utilization in the industry , and it is in conformity with the patent requirements . the purpose of the preferred embodiment described above is only illustrative , and it is not intended to be construed as to be any restrictions to the present invention . therefore , any variations or modifications made within the spirit and scope of the present invention can be included in the scope of protection of the attached claims .