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From: whit@milton.u.washington.edu (John Whitmore)
Newsgroups: sci.electronics
Subject: Re: Blue and UltraViolet LED's
Summary: Different colors are due to different semiconductors
Message-ID: <5206@milton.u.washington.edu>
Date: 18 Jul 90 01:08:28 GMT
References: <1990Jul11.233848.29098@zoo.toronto.edu> <1551@oucsace.cs.OHIOU.EDU> <38692@cci632.UUCP>
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Organization: University of Washington, Seattle
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In article <38692@cci632.UUCP> rdi@ccird3.UUCP (Rick Inzero) writes:
>
>...just what's so technologically difficult here, regarding UV LEDs?  
>Sure, the currently used plastic housings won't pass shorter 
>wavelengths of UV, but so what?  Wouldn't a silica glass housing work just 
>fine, in fact, even passing short wavelengths of UV?

	The light emission occurs preferentially at the bandgap energy
of a semiconductor.  GaAs gives infrared; Ga, Al, and In in some proportion
with As, P give various shades up to green.
	To get blue, SiC is used (that's silicon carbide, like 
the grit in sandpaper).  For UV, you'd need to develop yet another
(new) semiconductor.  Maybe doped diamond?  The bandgap is about
right for UV...

			John Whitmore