Android :: How To Make An Image Easier To Click?

I placed an image in each List View Item at the right side,In the layout xml,I set its width and length as 20dip ,kind of small,and I find it is hard to click at it cause the image only occupied 20*20 dip,I hope the length of it doesn't change,while its height full filling the parent,
I tried :android:layout_width="20dip"
android:layout_height="fill_parent"
but it doesn't work. Below is my xml:
<Relative Layout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/item"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="horizontal"
android:padding="6dip"
android:background="#FFFFFF">
<Image View android:id="@+id/avatar"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_margin Right="6dip"
android:src="@drawable/default_happy_face"/>