  The ground state phase diagram of 2D electrons in a high Landau level (index
N=2) is studied by the density matrix renormalization group method. Pair
correlation functions are systematically calculated for various filling factors
from v=1/8 to 1/2. It is shown that the ground state phase diagram consists of
three different CDW states called stripe-phase, bubble-phase, and Wigner
crystal. The boundary between the stripe and the bubble phases is determined to
be v_c = 0.38, and that for the bubble phase and Wigner crystal is v_c = 0.24.
Each transition is of first order.
