  We present deep 3.8 micron observations of the Trapezium cluster in Orion
obtained with the ESO VLT. We use these data to search for infrared excess
emission and evidence for protoplanetary disks associated with the faint,
substellar population of this young cluster, and to investigate the nature and
extent of a recently discovered population of deeply embedded sources located
in dense molecular gas behind the cluster. Examining the infrared colors of 38
luminosity and 24 spectroscopically selected substellar candidates we determine
an infrared excess fraction of 50+/-20% from the JHKsLp colors for both
samples. This finding confirms the presence of infrared excess, likely due to
circumstellar disks, around a significant fraction of the cluster's substellar
population. Our deep Lp imaging survey also provides new information concerning
the deeply embedded population of young objects located in the molecular cloud
behind the cluster; in particular, it doubles the number of sources in the
cluster region known to possess extremely red K-L colors. These objects exhibit
K-Lp colors indicative of deeply buried, possibly protostellar, objects that
likely mark the site of the most recent and ongoing star formation in the
region. We find the surface density distribution of the deeply embedded
population to follow that of the background molecular ridge and to be highly
structured, consisting of a string of at least 5 significant subclusters. These
subclusters may represent the primordial building blocks out of which the
cluster was and perhaps still is being assembled. These observations may thus
provide insights into the early stages of cluster formation and appear
consistent with recent simulations that suggest that the Trapezium cluster may
have formed from numerous but small primordial subclusters.
