HTML - PHP - AJAX send data issue

My HTML Code:

<form action="process.php" method="POST" class="appointment">
<input type="text" name="name" class="form-control" required="" placeholder="Adınız">
<input type="text" name="surname" class="form-control" required="" placeholder="Soyadınız">
<input type="text" name="phone" class="form-control" required="" placeholder="Cep Telefonunuz">
<input type="email" name="email" class="form-control" placeholder="eMail Adresiniz">
<select name="service" required="" class="form-control" onchange="getPersonnels(this.value);">
    <option value="">1) Lütfen hizmet seçin</option>
    <option value="1">Klinik Diyet</option>
    <option value="2">Online Diyet</option>
    <option value="3">Klinik Psikolojik Destek</option>
    <option value="4">Online Psikolojik Destek</option>
    <option value="5">Fitness</option>
</select>
<select name="personnel" required="" id="personnels" class="form-control" onchange="getPersonnelWorkingDays(this.value);">
    <option value="">2) Lütfen önce hizmet seçin</option>
</select>
<select name="date" required="" id="personnel-date" class="form-control" onchange="getPersonnelWorkingDaysHours(this.value);">
    <option value="">3) Lütfen önce danışman seçin</option>
</select>
<select name="clock" required="" id="personnel-date-hours" class="form-control">
    <option value="">4) Lütfen önce gün seçin</option>
</select>
<input type="submit" name="create-appointment" value="Randevu Oluştur" class="btn btn-secondary py-3 px-4">

And my js:

<script type="text/javascript">
function getPersonnels(val) {
    $.ajax({
        type: "POST",
        url: "/ajax.php?getPersonnels",
        data:'service='+val,
        success: function(data){
            $("#personnels").html(data);
        }
    });
}

function getPersonnelWorkingDays(val) {
    $.ajax({
        type: "POST",
        url: "/ajax.php?getPersonnelWorkingDays",
        data:'personnel='+val,
        success: function(data){
            $("#personnel-date").html(data);
        }
    });
}

function getPersonnelWorkingDaysHours(val) {
    $.ajax({
        type: "POST",
        url: "/ajax.php?getPersonnelWorkingDaysHours",
        data:'personnel'+val,
        success: function(data){
            $("#personnel-date-hours").html(data);
        }
    });
}
</script>

ajax.php include:

<?
if(isset($_GET['getPersonnelWorkingDaysHours'])){
    /* Test block, i'll code here when i catch the value */
    <option><? echo $_POST['personnel']; ?></option> 
}
?>

So you see, I want to catch value from name of "personnel" and id of "personnels", other functions are running when i request to the ajax page. But this function couldn't. I think this problem is caused by

data:'personnel'+val,

line of my js.

Whats your idea ? Thank you.