Abstract: Disclosed is a method of determining causes of intrinsic oscillations in a double-barrier quantum-well intrinsic oscillator comprising developing an emitter quantum-well (EQW) from a double-barrier quantum-well system (DBQWS); coupling the EQW to a main quantum-well (MQW), wherein the MQW is defined by double-barrier heterostructures of a resonant tunneling diode; using energy subband coupling to induce quantum-based fluctuations in the EQW; creating intrinsic oscillations in electron density and electron current in the DBQWS; forming a distinct subband structure based on the intrinsic oscillations; and identifying a THz-frequency signal source based on the quantum-based fluctuations, wherein the intrinsic oscillations comprise maximum subband coherence, partial subband coherence, and minimum subband coherence, wherein the energy subband is a quantum mechanical energy subband, wherein the intrinsic oscillations occur proximate to a bias voltage point in the range of 0.224 V and 0.