Quantum Well Electron Energy

[jendrix]

Homework Statement

For a GaAs with bandgap Eg =1.4eV

Effective electron mass is 0.07*me

d=10nm

Calculate the energy of the ground (lowest) electron level in the conduction band with respect to the bottom of the conduction band.

Homework Equations

Ea =Ec + h^2a^2 / 8*me*d^2

The Attempt at a Solution

As it was with respect to the conduction band bottom I only used the second part of the equation and as it was the lowest level I had a=1

My result

Put it through Wolfram so you can see working

http://i.imgur.com/xRbGy5f.png

However the answer I was given as a solution was

4.36*10^-21 J ( 0.027eV)in the book

where as my result is 8.6*10^-21

Is there something wrong with my method?

Thanks