填充数组中的数字

我有以下PHP代码创建数组A-MTP-1-1, A-MTP-1-2，等....

<?php
for ($i = 1; $i <= 3; $i++) {           # Pass 3 as you need three sets
    foreach (range(1, 12) as $val) {    # 1,12 again as per your requirements
        $arr[] = "A-MTP-$i-" . $val;
    }
}
foreach (array_chunk($arr, 4) as $k => $arr1) {    # Loop the array chunks and set a key
    $finarray["ch" . ($k + 1)] = $arr1;
}
extract($finarray);   # Use the extract on that array so you can access each array separately
print_r($ch9);        # For printing the $ch9 as you requested.
?>

我需要数组的个位数前面有一个0，这样它就会变成a - mtp -01-01, a - mtp -01-02，等等…但是当到达两位数时不能有零

我怎样才能达到我需要的，因为我已经尝试了以下，它没有改变:

for ($i = 01; $i <= 12; $i++) {           # Pass 3 as you need three sets
    foreach (range(01, 12) as $val) {    # 1,12 again as per your requirements
        $arr[] = "A-MTP-$i-" . $val;