NOVELTY - The crystal(s) containing defects and/or strain is placed in a pressure medium, and the crystal and the pressure medium are disposed in a high pressure cell. The cell is processed under reaction conditions at high temperature and high pressure for a specific time in a high pressure apparatus, and the defect(s) in the crystal are removed and/or the strain in the crystal is relieved.    USE - For removing defect(s), and for relieving strains, in non-diamond crystals for epitaxial structure used for semiconductor devices e.g. light emitting diode (LED), laser diode, photodetector, filter, transistor, rectifier, thyristor, light amplifier, emitter, detector, diode, switch, solar cell, and optically bistable device (all claimed). For removing voids, micro-pipes, nano-pipes, dislocations, interstitials, vacancies and strain defects in amorphous material such as glass, plastic, or metal.    ADVANTAGE - The obtained crystal enables to produce devices with high material quality and low dislocation density, and devices which are free from microvoids or nanovoids. The photo-voltaic detector produced using the crystal has excellent reverse leakage current density. The electronic devices produced using the crystals have increased breakdown fields, reduced leakage currents, increased thermal conductivity, higher light emission efficiency, and higher reliability.    DETAILED DESCRIPTION - The crystal is a boule, an electronic wafer, a window, a laser rod, and/or a sensor. The crystal is selected from direct bandgap semiconductor material, indirect bandgap semiconductor material, wide bandgap semiconductor material, scintillator material, non-linear optical material, laser material, relaxor ferroelectric material or piezoelectric material, or contains silicon carbides (6H-SiC, 4H-SiC, 15R-SiC, 3C-SiC, 8H-SiC, and 2H-SiC), silicon (Si), germanium (Ge), cubic boron nitride (cBN), gallium nitride (GaN), gallium antimonide (GaSb), aluminum nitride (AlN), aluminum gallium indium nitride (AlInGaN), bismuth antimonide (BxSb1-x), indium nitride (InN), gallium arsenide (GaAs), gallium phosphide (GaP), gallium indium phosphide (GaInP), aluminum indium phosphide (AlInP), indium aluminum arsenide (InAlAs), aluminum gallium antimonide (AlGaSb), indium aluminum gallium arsenide (InAlGaAs), aluminum indium gallium phosphide (AlInGaP), aluminum gallium arsenide (AlGaAs), indium gallium arsenic phosphide (InGaAsP), gallium selenide (GaSe), indium phosphide (InP), indium selenide (InSe and InSe2), indium antimonide (InSb), cadmium phosphide (Cd3P2), cadmium indium sulfide (CdIn2S4), cadmium silicon arsenide (CdSiAs2), cadmium tin phosphide (CdSnP2), zinc oxide (ZnO), zinc selenide (ZnSe), zinc telluride (ZnTe), cadmium sulfide (CdS), cadmium zinc selenide (CdZnSe), beryllium zinc cadmium selenide (BeZnCdSe), zinc cadmium magnesium selenide (ZnCdMgSe), zinc sulfur selenide (ZnSSe), beryllium zinc selenide (BeZnSe), beryllium magnesium zinc selenide (BeMgZnSe), cadmium telluride (CdTe), cadmium zinc telluride (CdxZn1-xTe), mercury cadmium telluride (HgCdTe), lead sulfide (PbS), lead telluride (PbTe), lead selenide (PbSe), lead tin telluride (PbSnTe), lead germanium telluride (PbGeTe), lead europium telluride (PbEuTe), lead europium selenide (PbEuSe), lead cadmium sulfide (PbCdS), lead europium selenium telluride (PbEuSeTe), lead sulfur selenide (PbSSe), lithium triborate (LiB3O5 or LBO), yttrium orthovanadate (YVO4), potassium titanyl phosphate (KTiOPO4 or KTP), potassium niobate (KnbO3 or KN), cesium lithium borate (CsLiB6O10 or CLBO), lithium calcium aluminum fluoride (LiCaAlF6 or LiCAF), lithium strontium aluminum fluoride (LiSrAlF6 or LiSAF), lead zirconium titanate (Pb(ZrxTi1-x)O3 or PZT), lead magnesium niobate (Pb(Mg1/3Nb2/3)O3 or PMN), lead zirconate niobate (Pb(Zr1/3Nb2/3)O3 or PZN), bismuth sulfoxide (BSO), barium titanate (BTO), lead magnesium niobate titanate (Pb(Mgx/3Nb2x/3Ti1-x)O3 or PMNT), lead zirconate niobate titanate (Pb(Zrx/3Nb2x/3Ti1-x)O3 or PZNT), strontium hafnate (SrHfO3) and barium hafnate (BaHfO3), rare earth lanthanide-ion laser crystals with matrices of silica, silicates and fluorozirconates, laser crystals based on matrices of potassium chloride (KCl), rubidium chloride (RbCl), sodium chloride (NaCl), copper chloride (CuCl), cesium iodide (CsI), calcium fluoride (CaF2), zinc fluoride (ZnF2), magnesium fluoride (MgF2), strontium fluoride (SrF2), manganese fluoride (MnF2), zinc sulfide (ZnS), zinc selenide (ZnSe), calcium fluoride-erbium fluoride (CaF2-ErF3), potassium iodide (KI), rubidium calcium fluoride (RbCaF3), lithium niobium oxide (LiNbO3), potassium magnesium fluoride (KMgF3), calcium chloro phosphate (Ca2PO4Cl), calcium-gadolinium-silicon complex oxide (CaGd2(SiO4)3O), lanthanum chloride (LaCl3), lithium yttrium fluoride (LiYF4), lanthanum fluoride (LaF3), yttrium aluminum mixed oxide (Y3Al5O12), lithium yttrium fluoride (LiYF4), aluminum oxide (LuAlO3), yttrium aluminum oxide (YAlO3), gadolinium gallium oxide (Gd3Ga5O12), calcium fluoride-erbium fluoride (CaF2-ErF3), erbium aluminum oxide (Er3Al5O12), lutetium aluminum complex oxide (Lu3Al5O12), barium ytterbium fluoride (BaYb2F8), sodium fluoride (NaF), lithium fluoride (LiF), sapphire, alexandrite, forsterite, lithium yttrium fluoride (LiYF4), barium fluoride (BaF2), barium yttrium fluoride (BaY2F8), barium erbium fluoride (BaEr2F8), rubidium bromide (RbBr), lithium germanium oxide (Li2GeO3), yttrium oxide (Y2O3), erbium oxide (Er2O3), yttrium vanadate (YVO4), gadolinium aluminum oxide (GdAlO3), yttrium-scandium-gallium complex oxide (Y3Sc2Ga3O12), sodium calcium erbium fluoride (NaCaErF6), calcium tungstate, or calcium molybdate.    INDEPENDENT CLAIMS are also included for the following:    (1) crystal having diminished defects or relieved strain;    (2) epitaxial structure;    (3) semiconductor device; and    (4) article.