Anyone know a good ranfom number generator for c# [duplicate]

This question already has an answer here:

• Random number generator only generating one random number 7 answers

So i'm trying to make a procedural cave generator in c# and so far i have the code for generating a completly random map:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Drawing;

namespace CelularAutomata
{
    class Program
    {
        static int width=512, height=512;
        Boolean[,] cellmap = new Boolean[width, height];

        static float chanceToStartAlive = 0.45f;

        public static Boolean[,] initialiseMap()
        {
            Boolean[,] map = new Boolean[width, height];

            for (int x = 0; x < width; x++)
            {
                Random rng = new Random();
                for (int y = 0; y < height; y++)
                {
                    doube random = rng.NextDouble();
                    if (random < chanceToStartAlive)
                    {
                        map[x,y] = true;
                    }
                }
            }
            return map;
        }

        public static Bitmap createImage(Boolean[,] map)
        {
            Bitmap bmp = new Bitmap(512, 512);

            for (int y = 0; y < height; y++)
            {
                for (int x = 0; x < width; x++)
                {
                    if (map[x, y])
                    {
                        bmp.SetPixel(x, y, Color.FromArgb(255, 255, 255));
                    }
                    else {
                        bmp.SetPixel(x, y, Color.FromArgb(0, 0, 0));
                    }

                }
                Console.Write('\n');
            }

            return bmp;
        }

        static void Main(string[] args)
        {
            Boolean[,] map = initialiseMap();

            Bitmap bmp = createImage(map);
            bmp.Save("C:\\Users\\radu\\Documents\\Sync\\Licenta\\chamber.png");
        }
    }
}

The image i'm trying to obtain is something like this, except in black and white:

What i'm getting is this:

I believe it's because of the random number generator i'm using (i.e. just Random().NextDouble()). Anyone know a beter RNG for c#?