GaAs would make for awesome switching systems, as it is a direct bandgap semiconductor, as opposed to Silicon, which requires phonon mediation. While this is a tremendous technological advantage, you have that minor problem of fabrication.
For GaAs, you need ~5 atmospheres of As gas at 550C. Not something anyone wants in their backyard, for good reason.
For InP, you need to worry about your supply of rare earth (In) elements, and all the surrounding tech needed to grow ingots of an appropriate orientation material for InP. You have to worry about the role of defects (which is what I simulated), how to dope, how to build structures.
Its not simply that it is technologically better, its that there is a whole massive ecosystem around Silicon, that for better or worse, pretty much guarantees that we are going to be running silicon based units for a long ... long time.
The joke, and there was one when I was in grad school, about GaAs and other non-Si materials was, they are the materials of the future. And always will be.
How do we break out? By gallium arsenide offering enough more than silicon does to be worth the effort. So far, that hasn't happened. It may never, except for small niches.
> Such a chip would replace 16 5GHz cores for more mainstream computation,...
80 GHz 6502 would be about as fast as... 1 GHz x86 in integer operations, and even that is being generous.
Floating point would be several orders of magnitude worse than even that.
Typical X86 can do 64 8-bit SIMD operations per clock, 2x AVX2 instructions retired in a single clock cycle. At over 4 GHz.
But it'd sure be a beast in real-time applications... assuming signal integrity is a solvable problem.
I'd be skeptical about whether it beats an FPGA.
So it would seem they beat FPGAs in some niches.
I question the 80ghz number given by the grandparent though. Looking at visual 6502 you're not going to get a order of better magnitude fanout on that design.
Better fanout than what?
The most useful thing I could find was this old article, but it certainly suggests that the room is there to expand: https://spectrum.ieee.org/semiconductors/materials/indium-ph...
I am angry for not having bought at least the 22i HD(high density) development kit, when it was available for 999USD for a time. But the software license was only valid for a year, so no-go.
They now offer embeddable FPGA IP cores targetting 750Mhz on TSMCs 7,12&16nm process.
And 'normal' FPGAs, the Speedster 7t, manufactured by TSMC at 7nm, also 750Mhz fmax.
All rather expensive and out of reach for the hobbyist :-(
It's a relative difference though, that depends on what material you're building the circuit in. If you can build an FPGA to run at 1/10th the speed of a 6502, then with a sufficiently expensive process you get a tradeoff between a very weak 80GHz processor and a customizable 8GHz circuit.
In the wings there are a few semiconductor materials, from Si-Ge to In-P and Ga-A and Ga-N that are used in optical transceivers, cell phone base stations, power electronics, and military electronics. Silicon is a good, not great superconductor, and it dominates because we are good at making things out of Silicon.
An In-P microprocessor as complex as a 6502 should be able to clock upwards of 80 GHz and could run with a fully populated address space of static RAM on the chip and be able to react to fast events in real time like nothing else.
Such a chip would replace 16 5GHz cores for more mainstream computation, so if cost gaps narrowed, the In-P part might compete with a Si part in a complex chiplet architecture. (e.g. the In-P chip can be built at 1/16 the density of the Si chip and not have all this multiple-patterning and lasers trouble that Si is getting into)