How to align a Text to the bottom - flutter

Question

I'm trying to build a very simple login page, and i want that the "sign up" text to be at the bottom of the screen.
I'm trying to align the text in the last column to the bottom of the screen, but somehow the aligment doesn't work.
When i try to use the Expanded widget, the IDE throw me an paint error.
class EmailLogin extends StatefulWidget {
#override
_EmailLoginState createState() => _EmailLoginState();
}
class _EmailLoginState extends State<EmailLogin> {
final Map<String, dynamic> _formData = {'email': null, 'password': null};
final GlobalKey<FormState> _formKey = GlobalKey<FormState>();
Widget _emailTextField() {
return TextFormField(
decoration: InputDecoration(
labelText: 'Email',
),
keyboardType: TextInputType.emailAddress,
},
onSaved: (String value) {
_formData['email'] = value;
},
);
}
Widget _passwordTextField() {
return TextFormField(
obscureText: true,
validator: (String value) {
if (value.isEmpty || value.length < 6) {
return "please enter valid password";
}
},
onSaved: (String value) {
_formData['password'] = value;
},
decoration: InputDecoration(
labelText: 'Password',
),
);
}
Widget _passwordConfirmTextField() {
return TextFormField(
obscureText: true,
validator: (String value) {
if (value.isEmpty || value.length < 6) {
return "please enter valid password";
}
},
onSaved: (String value) {
_formData['password'] = value;
},
decoration: InputDecoration(
labelText: 'Password',
),
);
}
void _submitForm() {
if (!_formKey.currentState.validate()) {
return;
}
_formKey.currentState.save();
print(_formData);
Navigator.of(context).pushNamed('/home');
}
#override
Widget build(BuildContext context) {
return Scaffold(
body: Stack(
fit: StackFit.expand,
children: <Widget>[
Image(
image: AssetImage("assets2/car.jpg"),
fit: BoxFit.cover,
color: Colors.black87,
colorBlendMode: BlendMode.darken,
),
SingleChildScrollView(
child: Form(
key: _formKey,
child: Container(
width: double.infinity,
child: Column(
children: <Widget>[
Padding(
padding: const EdgeInsets.only(top: 80.0),
child: Logo(),
),
Row(
mainAxisAlignment: MainAxisAlignment.center,
children: <Widget>[
Padding(
padding: EdgeInsets.only(top: 8.0, bottom: 80.0),
child: Text(
"Airbnb",
style: TextStyle(fontSize: 30.0),
),
),
],
),
Padding(
padding: const EdgeInsets.symmetric(horizontal: 20.0),
child: _emailTextField()),
SizedBox(
height: 15.0,
),
Padding(
padding: const EdgeInsets.symmetric(horizontal: 20.0),
child: _passwordTextField()),
Row(
children: <Widget>[
Expanded(
child: Padding(
padding: const EdgeInsets.only(
left: 20.0, right: 5.0, top: 10.0),
child: GestureDetector(
onTap: () {
_submitForm();
},
child: Container(
alignment: Alignment.center,
height: 60.0,
decoration: BoxDecoration(
color: Color(0xFF18D191),
borderRadius: BorderRadius.circular(10.0)),
child: Text(
'login',
style: TextStyle(
fontSize: 20.0, color: Colors.white),
),
),
),
),
),
Expanded(
child: Padding(
padding: const EdgeInsets.only(
left: 10.0, right: 20.0, top: 10.0),
child: Container(
alignment: Alignment.center,
height: 70.0,
child: Text(
'Forgot Password?',
style: TextStyle(
fontSize: 15.0, color: Color(0xFF18D191)),
),
),
),
),
],
),
Column(
children: <Widget>[
Container(
child: Text("switch to sign up"),
alignment: Alignment.bottomCenter,
),