The first thing that we have to take into account for this explanation is the basic principle in cosmic structure, which is Cosmic Entropy, consisting of a need to maintain the same energy density in all places and systems of the universe (Law of universal balance).

(To achieve this entropy, the cosmos uses magnetic force fields at different levels, from the high magnetic power that destroys systems, (large atoms such as uranium, and large stars such as supernovae), passing by through electromagnetic forces (+ /-) of orbital structuring, the weak forces, and even the thermal leveling forces that end up filling the atoms with their required energy.)

Well, the neutron is a semi-unstable particle that goes through a transit from the simple unstable particle P produced by an emission of particles, until it reaches its total stable state when it becomes a hydrogen atom.
This simple process would be the following:
When there is a significant emission of particles of very different dimensions, and among them some similar to the proton in dimension and mass, it initially has a significant level of positive untropy, that is, they have a high energy density for the small volume of the particle.
Therefore, it immediately produces positive electromagnetic fields around it, and as it rotates, it establishes a positive orbit that has the power to attract any orbital that is nearby.
If there are no nearby electrons, then it can also attract small particles that occupy this orbit and thus the volume of the system is established, already with the necessary entropy.
All this because an orbital system has been built with a great volume and a lower energy density than the single particle previously had.
But this system is quite imperfect and tends to be solved by successively joining all the smaller particles that the orbit contains, to end up becoming an electron and its corresponding neutrino. **(Pauli P.)
And so the system is finished and fully entropy balanced.
Well, this transit from when the unstable emitted particle P creates its corresponding electromagnetic orbit and captures the small particles it needs, until these particles become electron and neutrino, it is the life of the neutron as a particle with entropy, but imperfect for not have the electron common to all hydrogen atoms.

As we make clear in this process, all subatomic particles are composed of matter, which to achieve their entropy are grouped and distributed in stable systems of particles: Atoms, stars, electrons-neutrinos, planets-satellites, photons, galaxies, etc.
As we can see, the photon is included as a material particle with masses, with which we could in theory regroup them and form larger particles, including atoms.
I Hope, someday we will see.

** The Pauli principle is due to the fact that when many particles are established in an orbit, by action of gravity, they end up attracting each other and uniting to form a single orbital particle.

Antimatter does not exist, only particles equal in magnitude with different electric charges, (electron- and positron+; proton+ and antiproton-, etc.)
These particles do not annihilate each other when they come into contact (except for shocks at very high speeds), what they do is neutralize themselves by composing other types of particles or systems of particles in a state of electrical equilibrium and entropy.
An example is the union of a proton and an antiproton as seen in the drawing.

About the current theory on neutrons:

The current theory of neutrons says that (free or not) neutron is a compound of proton (+) and electron (-), but according to its behavior this would be illogical:
A proton (+) together with an electron (-) would be the most stable particle in the universe because it is the simplest possible union of a positive charge with a negative charge.
However, and according to current theory, (freely) it is unstable and emits an electron quickly.
But this assumption is not supported by any physical logic and of electromagnetic charges, since these simple proton-electron union would be indestructive and totally stable.
However, my model is different: Every large particle (for example, the size of a proton, or larger) creates powerful positive (+) magnetic orbits on which smaller orbitals such as electrons are attracted.
And as you can see that is what happens.
That is, positive charges reside not in the nuclei, but in the atomic orbits (or of large particles) on which orbital ones (or minor particles) are attracted, located and held, and so, in particles like proton-neutron-size, they already structure a powerful positive orbit that attracts (as in the neutron transition) to any electron within its reach.