Different Order of Magnitude on Distinct Interval Plot Axes

I have a function as defined below:

y[x_] := 9*10^-9*(Exp[x/(2*23*10^-3)] - 1)


I am trying to plot this function for the range -40<=x<0.7, but in the range [-40,0], the function has very small values so they are not visible when displayed with the values in the interval [0,0.7].

Actually, I want to put 10^-9 order of magnitude for y[x]<=0 corresponding to x<=0, and 10^-3 for 0<=y[x] which corresponding to 0<=x<0.7.

I'd also like to make the ticks on the positive y axis display whole numbers 1, 2, 3, .... and scale them by a factor of 10^-3.

Module[{f, p1, p2, opts, labels, nlist},
f[x_] := 9*10^-9*(Exp[x/(2*23*10^-3)] - 1);
opts = {Frame -> True, AxesOrigin -> {0, 0},
FrameTicks -> {{labels, None}, {Automatic, None}}};
nlist = Range[-2*^-8, 0, 0.5*^-8];
labels =
Riffle[nlist,
StringJoin[ToString[#],
"*\!$$\*SuperscriptBox[\(10$$, $$-9$$]\)"] & /@
Round[10*^9 nlist]]~Partition~2;
p1 = Plot[f[x], {x, -40, -2}, Evaluate@opts];
nlist = Range[0, 0.001, 0.0001];
labels =
Riffle[nlist,
StringJoin[ToString[#],
"*\!$$\*SuperscriptBox[\(10$$, $$-3$$]\)"] & /@
Round[10*^3 nlist]]~Partition~2;
p2 = Plot[f[x], {x, -2, 1}, Evaluate@opts];
GraphicsGrid[{{p1, p2}}]]