symeric double gate tunnel fet in silvaco

Dear all
I am working on Tunnel FETs. When I simulated a symmetric Double Gate TFET, I saw that the electric field and band to band tunneling rate isn't equal in the both channel surfaces. I have written same names for both gates according below:
go atlas
title Tunnel fet, dual gate, graded HJ (SiG)
#
mesh space.mult=1 width=1
#
x.mesh loc=0.000 spac=0.0005

x.mesh loc=0.100 spac=0.0005
#
y.mesh loc=0.000 spac=0.0005
y.mesh loc=0.020 spac=0.0005
#
# SECTION 2: Structure and models spectifications
#
width=1
region num=1 mat=oxide y.min=0.000 y.max=0.002
region num=2 mat=si y.min=0.002 y.max=0.018 x.min=0.000 x.max=0.1
region num=4 mat=oxide y.min=0.018 y.max=0.0200

elect name=source y.min=0.002 y.max=0.018 x.min=0.000 x.max=0.00
elect name=gate y.min=0.000 y.max=0.000 x.min=0.02 x.max=0.08
elect name=gate y.min=0.0200 y.max=0.0200 x.min=0.02 x.max=0.08
elect name=drain y.min=0.002 y.max=0.018 x.min=0.10 x.max=0.100
doping uniform conc=1e19 n.type y.min=0.002 y.max=0.018 x.min=0.08
doping uniform conc=1e20 p.type y.min=0.002 y.max=0.018 x.max=0.02
material EG300=1.12
models bbt.kl
contact name=gate work=4.74285
Could any one help me and let me know what the problem is. Please help and I will be forever grateful.
thanks