Low-temperature scanning-tunneling microscope for luminescence measurements in high magnetic fields

We have designed and built a low-temperature (1.3–4.2 K) scanning-tunneling microscope which is capable of collecting light that is generated in the tunneling region. Light collection is done by means of two fibers whose cleaved front is in close proximity $\mathrm{(\approx }\mathrm{1}$ mm) to the tunneling region. The whole system can be operated in high magnetic fields (11 T) without loss of optical signal strength. As a demonstration, we measured the electroluminescence spectra of an InGaAs quantum well at various temperatures. At 4.2 K, we found an electron-to-photon conversion factor that is three orders of magnitude higher than at room temperature.