PowerShell random file generator too slow

Trying to generate random files in Windows with this PowerShell script:

param([string]$path = "C:\temp", [int]$size = "1024", [long]$number= "1000")
Write-Host "Path: $path"
Write-Host "Size of file: $size"
Write-Host "Number of files: $number"

Write-Host "Started at:"
Get-Date -Format HH:mm:ss

md -Force $path |out-null

$script:StartTime = $(Get-Date)
for($i=0; $i -le $number - 1 ; $i++){
    [Byte[]]$out=@(); 0..($size-1) | %{$out += Get-Random -Minimum 0 -Maximum 255};
    [System.IO.File]::WriteAll("$path\$i.bin",$out)
    if (-Not ($i % 100) -and ($i -ne 0 )) {
        Write-Host "$i were created"
        $elapsedTime = $(Get-Date) - $script:StartTime
        $script:StartTime = $(Get-Date)
        Write-Host "$elapsedTime"
    }
}

When I want to increase filesize from 1KB to 1MB, it take a long time for even one file, but I need thousands of those. Is there way to solve this bottleneck?