Is there a better way to have my computer opponent to generate a word of (3 > random length <= 7)?

I have implemented the following method to do as such, but I still find that a lot of the times it produces only a three letter word. Once in a great while, it does do a four letter, five letter, etc. word, but it is still most three letters. Is there any other way that can guarantee a true random, to where it's always changing and never repetitive? Please let me know if I need to clarify myself further. This is for a Scrabble-like game, in which I am building for a final project in my Java programming class. TIA!

Here is my code:

//METHOD - getWordFromComputer
public static String getWordFromComputer(char[] let)
{
    Random rand = new Random();
    rand.setSeed(System.currentTimeMillis());
    String word = "";
    boolean done = false;
    while(!done)
    {
        word = "";
        boolean[] used = new boolean[7];
        int lettersUsed = 0;
        int max = 7;
        int min = 3;
        int size = rand.nextInt((max - min) + 1) + min;//Code provided by: mkyong.com
        while(lettersUsed < size)
        {
            int i = rand.nextInt(7); //Random from 0 to 6 (7)
            if(!used[i]) { //The current index hasn't been chosen yet
                used[i] = true;
                lettersUsed++;
                if(let[i] != '_') {
                    word += let[i];
                } else {
                    word += letters[rand.nextInt(26)];
                }
            }
        }
        if(wordVerify(word)) {
            done = true;
        }
    }
    return word;
}