How do I return clean JSON from a WCF Service?

I am trying to return some JSON from a WCF service. This service simply returns some content from my database. I can get the data. However, I am concerned about the format of my JSON. Currently, the JSON that gets returned is formatted like this:

{"d":"[{\"Age\":35,\"FirstName\":\"Peyton\",\"LastName\":\"Manning\"},{\"Age\":31,\"FirstName\":\"Drew\",\"LastName\":\"Brees\"},{\"Age\":29,\"FirstName\":\"Tony\",\"LastName\":\"Romo\"}]"} 

In reality, I would like my JSON to be formatted as cleanly as possible. I believe (I may be incorrect), that the same collection of results, represented in clean JSON, should look like so:

[{
  "Age": 35,
  "FirstName": "Peyton",
  "LastName": "Manning"
}, {
  "Age": 31,
  "FirstName": "Drew",
  "LastName": "Brees"
}, {
  "Age": 29,
  "FirstName": "Tony",
  "LastName": "Romo"
}]

I have no idea where the “d” is coming from. I also have no clue why the escape characters are being inserted. My entity looks like the following:

[DataContract]
public class Person
{
    [DataMember]
    public string FirstName { get; set; }

    [DataMember]
    public string LastName { get; set; }

    [DataMember]
    public int Age { get; set; }

    public Person(string firstName, string lastName, int age)
    {
        this.FirstName = firstName;
        this.LastName = lastName;
        this.Age = age;
    }
}

The service that is responsible for returning the content is defined as:

[ServiceContract(Namespace = "")]
[AspNetCompatibilityRequirements(RequirementsMode = AspNetCompatibilityRequirementsMode.Allowed)]
public class TestService
{
    [OperationContract]
    [WebGet(ResponseFormat = WebMessageFormat.Json)]
    public string GetResults()
    {
        List<Person> results = new List<Person>();
        results.Add(new Person("Peyton", "Manning", 35));
        results.Add(new Person("Drew", "Brees", 31));
        results.Add(new Person("Tony", "Romo", 29));

        // Serialize the results as JSON
        DataContractJsonSerializer serializer = new DataContractJsonSerializer(results.GetType());
        MemoryStream memoryStream = new MemoryStream();
        serializer.WriteObject(memoryStream, results);

        // Return the results serialized as JSON
        string json = Encoding.Default.GetString(memoryStream.ToArray());
        return json;
    }
}

How do I return “clean” JSON from a WCF service?
Thank you!